They were woeful tonight, but that's not all of their problems.
Wenger has significantly weakened Arsenal's defence and the attack. The defence is by far the worst aspect of the team, and this is due to his poor decisions in the last transfer window. They're now scraping the barrel for defenders after only a handful of games... after Wenger let several go over the summer. With Debuchy injured, Arsenal are crying out for replacement - and the man that could meet that need is Carl Jenkinson, who finds himself on loan at West Ham. Up front, they have Danny Welbeck, Yaya Sanogo and Olivier Giroud - a far worse strikeforce than any of the clubs around them. Giroud is horribly inconsistent, Danny Welbeck averages 1 goal every 4 games (and that's with some of Europe's best players creating chances for him) and Sanogo averages 0 goals ever, unless they're in a preseason friendly.
Wenger even said himself that he wanted to sign Welbeck on loan... but instead of ensuring that happened, left on the final day of the transfer window to referee a charity match abroad, letting the board take over. He also had first refusal on Cesc Fabregas over the summer, and turned him down - which was a terrible, terrible decision. Fabregas could walk into Arsenal's team right now - but instead, he's busy winning the league with Chelsea.
Wenger never replaced Henry or Vieira, and the club have suffered for almost ten years because of this - with minimal success during that time for a club of their stature and transfer budgets. One trophy in what, eight years? Not good enough.
Wenger's time at Arsenal's helm should come to an end in May, and if I was the Arsenal board, I'd have my eyes on Jurgen Klopp - the manager of Arsenal's opponents tonight. Arsenal will never be a threat to the top teams under Wenger again, and the only way for Arsenal is down under his management. Klopp would be an excellent addition, should he wish to join. Arsenal need new life breathing into them, as under Wenger, they've become stagnant and have lost considerable ground on the other top teams.
What say you, @Viazon and @Enygma?