The Champions League group stage is underway, with Chelsea defending their title and 31 other clubs seeking to emulate them come May in Saint Petersburg, Russia. Following an exciting first round of games, we asked James Olley, Julien Laurens and Tom Hamilton to answer some big questions.

What caught your attention on Matchday 1?

Olley: Top forwards hitting the ground running. Manchester United may have lost but Cristiano Ronaldo continued his goal-scoring form in Tuesday's shock 2-1 defeat at Young Boys, before Romelu Lukaku and Robert Lewandowski followed suit later that night. Chelsea needed Lukaku's 69th-minute header to find a way past a spirited Zenit St Petersburg side while Lewandowski netted a brace in an easy Bayern Munich win at Barcelona. Wednesday saw more of the same with Mohamed Salah scoring for Liverpool, Erling Haaland finding the net for Borussia Dortmund and Manchester City's £100 million summer signing Jack Grealish marking his debut in the competition with a fine strike against RB Leipzig. Jules may have to wait for Paris Saint-Germain's "MNM" strike force to join the party but otherwise it felt like business as usual which, on a wider note, left me with a feeling of how quickly people forget.

Five months ago, the Champions League's very existence was threatened by 12 teams attempting to create a European Super League yet after that project collapsed, many of them simply began another campaign pursuing a Champions League title their earlier actions sought to devalue. In fact, only last week Barcelona president Joan Laporta claimed the Super League "is not dead yet" with Real Madrid and Juventus also still yet to give up on the idea being revived in some form. The players were unperturbed, of course, as we've seen with many of the leading stars delivering in an exciting week's action, but there remains something not quite right about several teams taking part in a competition they are still actively plotting to destroy.

Laurens: It has to be the "MNM" finally making their highly anticipated debut for PSG in Belgium against Club Brugge. On paper, the magical trio of Lionel Messi, Neymar and Kylian Mbappe is very tasty and has everything to become one of the best ever. They will need a bit of time and we saw on Wednesday night that they were not ready just yet: Messi and Neymar are not full match-fit, Mbappe came off early in the second half with a slight injury. They tried to combine and we could see that it should not take too long before they click properly. However, we also saw an unbalanced PSG team at times where the front three didn't defend and left their midfield and defence really exposed.

This PSG is a work in progress and they are probably quite lucky to have got a point in Belgium because Brugge put them under real pressure. Mauricio Pochettino has to find the right formula to make the "MNM" trio and the rest of the team a force. At least they have two more weeks to work and improve before facing Pep Guardiola and Manchester City at the Parc des Princes.

Hamilton: There were many box-office moments in a remarkable first round, but there were two standout factors for me. Firstly, how wonderful it is to have fans back. I know this is a phrase which has been said frequently this season, but you really felt the impact in the Champions League. The Young Boys' faithful created an electric atmosphere at the Wankdorf Stadium for their win over Manchester United while at Anfield, Liverpool thrived off their vocal home support to start at 100 miles per hour against AC Milan. And at Brugge they created a superb claustrophobic welcome for PSG at the Jan Breydel Stadium.

But one other thing that stood out was some of the goalkeeping on show. There were some remarkable stops, from experienced Champions League keepers like Barcelona's Marc-Andre ter Stegen -- who pulled off two superb first-half saves to deny Bayern's Leroy Sane -- while the double save from Milan's Mike Maignan's off Salah's penalty and Andy Robertson's follow-up was special. Over at Malmo, their keeper Ismael Diawara did brilliantly to keep Juventus at bay in the second half, but if you're looking for the best of save the bunch, then Borussia Dortmund's Gregor Kobel pulled off an incredible reflex stop to prevent Besiktas' Michy Batshuayi from scoring in the first half of the German side's 2-1 win in Turkey. While some of the defending across the first matchday was suspect, the standard of goalkeeping was through the roof.

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Which big clubs have their work cut out to reach the knockout rounds?

Hamilton: Barcelona were comprehensively outplayed against Bayern Munich. Losing to the reigning Bundesliga champions is no embarrassment, but for a club of Barcelona's expectations -- despite their summer upheaval -- their opening performance in Group E was desperate. For the first time in their Champions League history they went a whole match without registering a single shot on target, and the humbling 3-0 defeat could have been far more one-sided but for the performance of Ter Stegen in goal. There were question marks wherever you looked with this Barca side, from their lack of firepower and creativity up front, to their meek defending where Eric Garcia's decision to turn his back on Thomas Muller's ambitious first-half effort proved to be a costly call.

The Barca faithful are growing restless, and even booed their very own Sergi Roberto. "I would like to remind people that he is a midfielder, not a winger," Gerard Pique said afterwards, defending his teammate. "He has made a sacrifice to adapt to that position on the pitch. People are free to express themselves but I do not like the whistles, they do not help. I know the person, he is a spectacular human being and he wants more than anything for this club to be successful. I am hurt a lot by this."

Olley: No one will be panicking after one game but the manner of Barca's defeat underlines the magnitude of the task the Catalans have in staying competitive at this level after all their recent upheaval. Tom's outlined that in good detail so I'll highlight Manchester United instead. It would still be a shock if they didn't progress but losing to Young Boys puts them on the back foot in Group F, although Villarreal and Atalanta playing out a 2-2 draw in Spain mitigates some of the damage.

But questions were inevitably raised about Ole Gunnar Solskjaer's tactical acumen as United were overwhelmed following Aaron Wan-Bissaka's 35th-minute red card. United were utterly overrun in midfield, an issue Solskjaer should have addressed sooner than he did despite the numerical disadvantage but at least the fixture list provides an opportune moment for redemption. Villarreal visit Old Trafford next, four months after beating United on penalties in last season's Europa League final. Unai Emery is a master of that competition but United failed to take their chances that night when they were in the ascendancy. They can't really afford a repeat.

Laurens: I think, despite their draw in Belgium, PSG will go through but it won't be easy. However, I am a bit worried about Atletico Madrid. They were disappointing again in this competition, drawing 0-0 at home against Porto on Wednesday like they did against Lokomotiv Moscow last season. They actually could not beat the Russian side in the reverse fixture either (1-1). Now they will have to play AC Milan and Liverpool twice, meaning they could find themselves in a bad position before facing Porto again in Portugal in Matchday 6 in December.

Despite all the attacking power they have (Luis Suarez, Antoine Griezmann, Angel Correa, Joao Felix, Yannick Carrasco, Thomas Lemar...) they still struggle to create chances and score goals. They have only scored four goals in their last seven Champions League games, including none in each of their last three. With Diego Simeone, we are never too far from the back six we saw against Chelsea in the round-of-16 first leg last season and I don't think this is good enough for such a talented squad. Simeone will have to find a way to make this work because otherwise the Spanish champions could be in trouble in this difficult and dangerous group.

The most exciting player, age 21 or under, in this season's competition is:

Laurens: We have an incredible clutch of 18-year-old prodigies, more than we have ever had before. Pedri, Jude Bellingham, Eduardo Camavinga, Giovanni Reyna, Jamal Musiala, Harvey Elliott, Benjamin Sesko, Ilaix Moriba are all still 18, as are Rayan Cherki and Florian Wirtz who are playing Europa League football this season. Ryan Gravenberch has turned 19 like Ilya Zabarnyi, Karim Adeyemi and Nuno Mendes while Ansu Fati (18) is still not back from his terrible injury.

So there is plenty to choose from but there could only be one winner for me and it's Bellingham. He was sensational against Besiktas on Wednesday. He is getting better and better, week after week. Marco Rose will help him develop and really the sky's the limit for the England international who is as mature as he is gifted.

Hamilton: Juls has done a fine job of picking out some of the best young talent, but for me three stood out from the first batch of games. Musiala was immense for Bayern Munich and had Barcelona's defence on a piece of string. And I would have gone for Bellingham here after his incredible performance against Besiktas where he controlled just about every facet of the game, and even scored their opener.

But in the interests of variety, I'll go for Salzburg's Karim Adeyemi. The young striker was outstanding against Sevilla and caused them all sorts of problems. He's a tricky, elusive sort of attacker who can also play on the flanks, and his high-octane brand of hectic football saw him win three first-half penalties against the LaLiga side. Salzburg have a fine record of seeing their top young talent making an impact in the Champions League since first qualifying three years ago and then earning big-money moves. We saw Haaland explode onto the scene in the 2019-20 campaign, while Dominik Szoboszlai was outstanding last term, and it looks to be Adeyemi's year this time around.

Olley: No prizes for originality here but it has to be Haaland given the wider context. The 21-year-old has a release clause of around €75m which comes into effect next summer, triggering what is likely to be the mother of all transfer scrambles for his signature. There is already little doubt over his quality given a staggering goal record for Dortmund -- he scored his 66th goal in 66 games on Wednesday, his 21st in 17 Champions League matches -- but another logic-defying season in Germany will only cement his status as the best young player in world football.

Chelsea were keen prior to signing Lukaku but Manchester United, Manchester City, Real Madrid and Paris Saint-Germain are just four of the clubs with a serious interest in Haaland next year. Agent Mino Raiola holds all the aces. The most unpalatable aspect of any agreement is likely to be the exorbitant fee Raiola can charge but a continuation of Haaland's own remarkable numbers will surely convince at least one club he's worth every penny.

In the Champions League era, which was the best team not to win it?

Laurens: The Arsenal "Invincibles." No debate. This is one of the greatest teams to ever play this sport, one of the greatest squads ever assembled and 2003-04 should/must have been their year in the Champions League like it was their year in the Premier League, where they won the title by going the whole season unbeaten. It was the perfect time, as none of the historically big European clubs were very good. The semifinals were Chelsea vs. Monaco and Porto vs. Deportivo La Coruna, and Jose Mourinho's Porto went on to win it.

The Gunners were knocked out by Chelsea in a dramatic quarterfinal second leg at Highbury. After drawing 1-1 at Stamford Bridge they managed to squander a 1-0 lead at home to lose 2-1 and go out. Maybe they were too confident about going through, maybe Arsene Wenger could have managed the game differently. In the end, a team with Patrick Vieira, Sol Campbell, Thierry Henry, Robert Pires and Dennis Bergkamp all at their best should have put their hands on the Champions League trophy.

Hamilton: There have been a few tales of Spanish sides who should have won a Champions League, like Real Madrid's Galactico's (2000-2006), Atletico Madrid's 2013-14 side, perhaps the latter stages of Johan Cruyff's Barcelona tenure (1993-96), but that glorious Valencia side of 1999-2001 had two chances to become champions of Europe and squandered both.

The team that lost the 2000 final to Real Madrid had Santiago Canizares in goal, Manuel Pellegrino, Jocelyn Angloma and Gerardo at the back, with the imperious Gaizka Mendieta running the show from midfield alongside Kily Gonzalez and Gerard. Then up front it was Claudio Lopez and Miguel Angulo. That year they'd already done for Barcelona and then Serie A champions Lazio in the knockouts, only to fall 3-0 to Los Blancos in the final. The following season Pablo Aimar, Robert Ayala, Diego Alonso, and John Carew were all added to the mix and went on another run to the final, knocking out Arsenal and Leeds en route only to lose to Bayern Munich on penalties. That era under Hector Cuper was a missed opportunity and though they'd go on to win the UEFA Cup and LaLiga under Rafa Benitez in 2003-04, the Champions League remains elusive.

Olley: All good selections above, but if Manchester City don't win the Champions League under Pep Guardiola his time in England will forever feel incomplete. Guardiola's City have already carved out a place in the pantheon of Premier League greats after securing three titles in four seasons playing some of the best football England has ever witnessed. Yet the Champions League continues to elude him. Three successive quarterfinal defeats -- often featuring odd tactical tweaks where Guardiola has almost over-complicated their approach -- preceded a run to last season's final where they were unable to produce their best against a Chelsea team riding the crest of a wave following Thomas Tuchel's arrival.

Missing out on signing Tottenham Hotspur striker Harry Kane this summer leaves an obvious hole in City's team up front but they still possess a raft of long-serving players -- Kevin De Bruyne, Raheem Sterling and Fernandinho among them -- who deserve a Champions League medal for their efforts over recent years. And even without Kane, they are among the favourites once more given the financial impact of COVID-19 has shifted the needle even further towards those with the richest of backers.