I saw him play at the Emirates last week against Dortmund. In all his games with Barca, I never saw a game where he made so many bad passes.
That said, he was the best player on the field. The shot he scored on was as good as it gets. He was very active getting into scoring position the entire game. His defense was astonishing, you just don't ever see a forward play that much defense, he was popping up all over the field.
Arsenal is a much better club for him than Barca was. His talent and energy really stand out at that level, whereas several Barca players were clearly better.