There's 2 ways you can look at our current situation.
1) We are in transistion - some players are past thier best and need replacing
This is the popular view and too be honest, I share it. Players like Freddie, Sol, Pires look a shadow of thier former-selves. They are past it IMO, living on their reputations. We have replacements in the squad, Walcott, Senderos, Hleb but they are not ready yet to replace them long term. However, on the plus side, experiences like last night will do them good in the long run.
Wenger has to come for some criticism as well, selling Paddy was all fine by me, but ONLY if a quality replacement was signed at the same time. This didn't happen for 1 reason or another, but letting him go after Edu had left was unforgivable. Paddy may well have had shite 18 months prior to leaving, but a below par Vieira is better than no Vieira at all! Wenger left the midfield too weak and we all knew it.
2) We have had terrible luck with injuries in defence.
To lose our first choice left back through injury, then our very capable second choice left back within a week is bad luck. Even the thrid choice left back (Cygan) is injured now. Its not much better over the other side, Lauren has been in and out (currently out for a month) Eboue is away at the ACN, and Gilbert the thrid choice limped off last night. We have no-one else left to play there. Campbell is not right at the moment too and no-one could have forseen the problems we have had in this area.
On a plus note, I really like the look of Djourou. He is commanding, good in the air, can pass well and looks like he has a good future in the game, lets hope he gets a run of games so he can make it at Arsenal.
IMO the current situation is down to a combination of the above, to lose Cole\Clichy has been detrimental to our attacking strength down the left side, we just don't look as dangerous coming forward without either of them in the team. Can't wait to get them back.
Still it looks like the run-in will be exciting!