Ole Gunnar Solskjaer takes charge of his 100th game as Manchester United manager when Arsenal visit Old Trafford on Sunday. It has been a rollercoaster ride for the Norwegian since he replaced Jose Mourinho, initially on an interim basis, in December 2018.

There have been incredible highs, such as the dramatic Champions League victory against Paris Saint-Germain in March 2019, and humiliating lows, as recently as the 6-1 defeat at home to Mourinho's Tottenham in the Premier League earlier this month. In 2020 alone, Solskjaer has taken United back into the Champions League, but guided the team to defeats in three cup semifinals. He has overseen the emergence and development of homegrown talent, including Marcus Rashford and Mason Greenwood, but he's also struggled to build a convincing defence and overall team unit.

So as Solskjaer prepares to hit the century mark as United boss -- winning 56 of his 99 games so far -- how does he measure up? Are United back on track under their former player, or going round in circles? ESPN has attempted to find an answer.

The positives

Nurtured young players

From the outset, Solskjaer has placed his trust in United's homegrown young players. It began with reviving Rashford after the England forward's difficult time under Jose Mourinho and has extended to giving sustained opportunities to Scott McTominay, Brandon Williams and Greenwood.

Louis van Gaal was similarly trusting of United's youngsters during his two-year spell in charge, but the Dutchman gave chances to too many who weren't good enough. Solskjaer has been able to filter the good from the indifferent, and United now have a nucleus of young players who can provide the team's foundation for the years ahead.

Made successful signings

United's player recruitment in recent years has been a recurring problem, with the club lurching from one expensive mistake to another, particularly during Van Gaal's tenure. But while Solskjaer has not landed all of his targets, the vast majority of his signings have improved the team and been recruited within a clearly thought-out strategy.

Centre-back Harry Maguire and right-back Aaron Wan-Bissaka have improved United defensively, while midfielder Bruno Fernandes has transformed the team in the attacking third.

Under Solskjaer, signings have been made with an obvious role to fill and although that may seem like a basic requirement, it wasn't always the case prior to his appointment.

Ditched underperforming stars

Solskjaer inherited an imbalanced squad from Mourinho, which included too many players who were simply not living up to expectations, and has ruthlessly ditched those who did not fit his blueprint for United.

Romelu Lukaku has scored 41 goals in 57 games for Inter Milan since leaving United in 2019, but the Belgian was out of form and blocking Greenwood's path to the first-team, so the manager made a big call -- and the right one -- by letting him go. Alexis Sanchez was also dispensed with after a disastrous 18 months at Old Trafford -- joining Lukaku at Inter -- while Marouane Fellaini, who had been a good servant for United, was allowed to depart for Shandong Luneng because he jarred with Solskjaer's football philosophy.

Chris Smalling (Roma), Ashley Young (Inter), Matteo Darmian (Parma) and Antonio Valencia (released) have also been offloaded as Solskjaer has attempted to remould the squad.

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Changed the mood

Old Trafford had become submerged in negativity by the time Mourinho was sacked, which meant Solskjaer's first task in charge was to change the mood on and off the pitch. He did that instantly with a run of 11 wins from his first 12 games in charge -- a sequence that transformed the atmosphere inside the dressing room and among the supporters.

There have been ups and downs in terms of results since those early days, but the mood has largely remained positive and there is a sense of unity in and around Old Trafford again.

Restored United's DNA

United under Solskjaer are clearly still a work in progress, but he's done something that none of his immediate predecessors (Mourinho, Van Gaal and David Moyes) were able, or prepared, to do: he has got the team playing United-style attacking football again. It doesn't always work, as some of United's results under the Norwegian prove, but there is now a sense that the team will play on the front foot rather than adopt the safety-first approach of Moyes, Van Gaal and Mourinho.

There have been precious few memorable, or exciting, moments for United since Sir Alex Ferguson retired in 2013, but virtually all of them have come under Solskjaer.

The negatives

Inconsistency

Almost two years into the job, Solskjaer has been unable to eradicate the wildly inconsistent form that has generated such extreme highs and lows.

United have had incredible runs under Solskjaer -- 11 wins from 12 in 2018-19, going unbeaten in 14 games to finish third at the end of last season -- but there have also been alarming slumps, including two wins from nine at the start of last season (United's worst-ever Premier League start) and eight defeats in 12 games in all competitions at the end of the 2018-19 campaign. On paper, this season looks to be an improvement, with six wins from nine games, but the two defeats, against Crystal Palace and Spurs, have seen them concede nine goals.

United blow hot and cold under Solskjaer, with seemingly nothing in between.

Tactics

Wednesday's 5-0 Champions League win against RB Leipzig, when Solskjaer deployed a diamond formation in midfield and made a series of successful substitutions, was a rare example of the Norwegian winning the tactical battle against his opposite number.

On too many occasions, Solskjaer has been outsmarted, and the biggest cause for alarm is his inability to act when things are going wrong. Just this season, the home defeats against Palace and Spurs have seen United go from bad to worse after falling behind, and the looks of confusion among the players on the pitch highlight the need for better direction from the manager.

A top coach makes changes to alter the course of a game in a positive manner. That rarely happens with Solskjaer.

Managing upwards

Solskjaer has been able to get rid of the players who have failed to perform, but he is stuck with the executives who have repeatedly let him down in the transfer market. Despite this unfortunate reality, Solskjaer has to learn how to successfully apply pressure on the likes of executive vice-chairman Ed Woodward and transfer negotiator Matt Judge to deliver.

Solskjaer had verbally agreed a deal with FC Salzburg striker Erling Haaland last December, but it fell through because Woodward and Judge failed to seal the transfer, allowing Borussia Dortmund to sign him for a meagre fee of around €20m instead. Haaland has gone on to score 23 goals in 26 games for his new club.

This summer, Solskjaer has seen Woodward and Judge fail to sign top targets such as Dortmund winger Jadon Sancho, Aston Villa midfielder Jack Grealish, RB Leipzig defender Dayot Upamecano and Birmingham midfielder Jude Bellingham.

Solskjaer does not challenge his bosses as openly as Mourinho and Van Gaal did, and to some United supporters, his failure to do so hints at a weakness in the manager's armoury.

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No obvious plan

After 99 games, we still don't know Solskjaer's plan to take United back to the top. He has used a 4-3-3 formation, played with three at the back and deployed a diamond in midfield, but it seems as though he is still trying to work out what best suits his players. It's difficult to imagine the likes of Pep Guardiola, Jurgen Klopp, Mourinho or Mauricio Pochettino still not knowing their best approach after 99 games in charge, but whenever United play, it is a guessing game as to how they will line up.

Certainty is the only way to success, but confusion still reigns under Solskjaer.

Verdict

For every positive with Solskjaer, it is easy to counter with a negative. He has done many good things in his time in charge, and it points to the lack of direction at the club prior to his arrival that United have been so hard to predict under him.

Even now, 99 games on, he is still having to unpick the bad decisions made by previous regimes. But after nearly two years, there really should be a clearer road map developing than the one we have right now. The defence still needs reinforcements and the midfield remains a puzzle due to the contrasting qualities of the players Solskjaer has at his disposal. From an attacking perspective, United can threaten even the best opponents, but when their counter-attacking approach does not work -- particularly against weaker teams -- they lack a Plan B.

Ultimately, United are in a better place now than when Solskjaer arrived, but it has been slow and frustrating progress. And even though they hammered Bundesliga leaders RB Leipzig on Wednesday, it would be no surprise to anybody if United slip up against Arsenal on Sunday.

It has been two steps forward and one step back for large periods of Solskjaer's reign and as he prepares for his 100th game, that still remains the case.