If this season had ended near the end of February, it would've probably been Arsenal and Wenger's most successful season since the Invincibles (2004-05).
At the end of February, Arsenal found themselves a single point behind Manchester United in the league, and on a run of five wins and a draw in their last six games. They were in the Carling Cup final versus struggling Birmingham City, with their first trophy in six years so close that it is possible that half the Arsenal squad could already taste it. They were still in the FA Cup, with a replay versus Leeds United coming up. And most impressively, Arshavin and Van Persie's late-game heroics had given Arsenal a 2-1 win over Barcelona in the first leg of their Champions League tie.
Unfortunately, Arsenal would go on to lose the Carling Cup final due to atrocious defensive communication between Koscielny and Szczesny, and from there, everything collapsed.
Arsenal picked up only two more league wins all season long, falling from second to fourth behind Chelsea and Manchester City. They were beaten in the FA Cup by Manchester United, and didn't even put up a fight versus Barcelona in the second leg at the Camp Nou, neither before nor after RVP's controversial sending off.
Quite honestly, from March to May, Arsenal looked like a team in shambles, a shadow of the team that was clicking so well and looked to finally have overcame its label as nothing more than a training ground for promising youth.
With competition getting ever tighter and harder in the Premier League, Wenger will have to be on the ball this coming season to make sure Arsenal can once again become the title contenders they were prior to February, or at the very least, that they don't get replaced in the top four by Tottenham or Liverpool. The following are the five things he'll need to work on this offseason to make this happen.