I like their 4-2-3-1. Cesc had an off-year but will be better next season after he's rested.
I'm not sure if either Milito would be good for the Prem. Diego is too slow (not to mention he's old), and Gabriel is very small. People keep on saying Arsenal need a commanding, large CB who is good on set pieces (although I think they're fine with TV5 and Djorou).
Honestly I'm not sure what they should do. Their starting XI is fine as it is. I think their only problem is they don't have an adequate replacement for RVP when he is hurt. Bendtner and Chamakh are both plan B's, but they need a great finisher who can be RVP's backup. I guess Milito could be that, since he's pretty good in the air too, especially if they can get him for 5 million quid (what other proven striker could they get for that in this market?). On the wings they have Nasri (great), Walcott (fast, English, and improving), Arshavin (had a bad year but is a great player, should be back), Vela (potential), Rosicky (experience). At DM I like the starting combo of Song and Wilshere, and Diaby and Denilson are capable backups (and there's Frimpong to think of). They have 4 good CB's. Two good RB's. If Gibbs is healthy they have a young, promising, fast, English LB, and Clichy is a capable back-up.
The squad is fine, they just had terrible timing with the CC final, Barca second leg, and OT FA Cup draw all in the same week. Losing that CC final destroyed their confidence, and the next two defeats (which were tough, tough games) meant they were ****** in the heads. The "no trophy" criticism has gotten to them and they really underperformed down the stretch at the end of the year. But I think the team is well-built and well-coached and they're fine. They just need to be confident next season and not let the criticism/lack of trophies/underconfidence get into their heads.