It's another defeat, and It closed Arsenal's title chance. Chelsea had lost a day before, and Arsenal would be back in race IF arsenal win. The first half, Arsenal leaded 1-0 and extended their lead, 2-0 in the beginning on the second half, by Mikael Silvestre's header. But that's all, and Wigan took the control of the game and Arsenal didn't defended well. Clichy, Silvestre, and most notably Lukasz Fabianski made mistakes, and it's ended with 2-3 defeat.
It's another prone defending who makes Arsenal lost. Almost every loss suffered by Arsenal is caused by bad defending, from losing 1-2 from Man.Utd, 0-3 from Chelsea, then FA Cup exit by Stoke 1-3. Then, the 1-3 and 0-2 defeat from Man.Utd and Chelsea is also caused by some bad defending. Then 1-2 from Porto, 1-4 from Barcelona, 1-2 from Tottenham, and the last is 2-3 from Wigan. Don't forget 1-1 draw against Birmingham. It's all about bad defending. Without disrespect other teams ability, Arsenal would have got better result.
Arsenal undoubtedly need to strenghten their squad, especially the defensive force. The need-to-improve position is Defensive Midfielder, Goalkeeper, and also Center Back. Maybe Arsenal need a central forwarder, but if Marouane Chamakh has agreed a contract with Arsenal, there would probably not buying another central forwarder.
On the defensive Midfielder, Arsenal has a good defensive midfielder in Alex Song. However, there's no backups for Alex Song. Arsene Wenger always believe Denilson to replace Song, and if Song and Denilson is absent, the water-carrier position is given to Craig Eastmond. Denilson is a potentially-good player, but he isn't a defensive midfielder. He is physically not too strong, and he is more like a playmaking central midfield. Craig Eastmond is still too young to play on the highest level. Maybe Anthony Annan (Rosenborg / Ghana); Blaise Matuidi (St. Ettiene / French), who has already expressed his desire to play under Wenger; and Moussa Sissoko (Tolouse / French), is a possible transfer
Then Goalkeeper position, Almunia has been up and down this season, but still much better than second goalkeeper, Lukasz Fabianski. Vito Mannone is still lack of experience. Fabianski could be offloaded due to error prone. Sergio Asenjo (Atletico / Spain) would be perfect, and could be 1st goalkeeper, replacing Almunia. Sebastian Frey (Fiorentina / French) also reportedly being linked to Arsenal but it's unlikely for Frey to move.
The weakest position is the center back. Thomas Vermaelen is world class, William Gallas is strong, Campbell is dependable, but Mikael Silvestre is the main weakness! He is always been prone error, alongside Fabianski. Well, Silvestre is likely to offloaded in the end of season, while Gallas' contract is runing out and some clubs like AS Roma, and PSG has already declared interest. Campbell would renew his contract, but Arsenal still need another Central Defender, if Gallas leave or not. Mamadou Sakho (PSG / French), Frederico Fazio (Sevilla / Argentina), or Brede Hangeland (Fulham / Norway) would be great transfer for Wenger
Reportedly Wenger has 45 millions pounds to spend this summer, so Wenger should buy something, or Arsenal would probably have another title-less season..