Considering that this is his first season in a new Country, a new culture, a new League and a new team I think that's he's okay overall. Not to forget that he's used to having 1-2 week winter breaks in La Liga where the pace is already a lot slower and there are more stoppages in play thanks to the "gamesmanship" attitude over there. Also the BPL is the most competitive league without a doubt, and this season is another great example of that.
I won't lie, the past few months his performances have been quite poor overall, but what people seem to forget is that Mesut Ozil is at his best when his attacking team-mates are making dangerous runs. He seemingly hit the ground running earlier in the season no thanks to players like Ramsey & Walcott constantly making runs. Even if he didn't pass to them, their runs made space for others like Wilshere & Giroud (who scored most of his goals during that time as well) who would benefit too. At Madrid he had Ronaldo, Benzema & Di Maria making runs around him which almost always resulted in a goal.
He's starting to pick up a bit now. The first 15/20 minutes against Bayern last night. Liverpool in the FA Cup and Man Utd before that. However, if you noticed that also tied in with Chamberlain's return from injury. Ozil needs these players around him.
I'm confident that he'll have a much better second season without question. The man is undoubtedly world-class.