Fun, and the two lead performances do mostly carry it though I feel like Robert Downey Jr is having a lot more fun as Tony Stark than here and Rachel McAdams does drag things down when she's on screen. The script isn't great, the story is never as good as the rest of the movie, and while the set-pieces are good they eventually overstay their welcome in almost every case. The whole thing is too long for the story, basically, which didn't want more than an hour to ninety minutes in the telling and would have been a better episode of a Holmes TV series than a movie. I feel like the boxing match is kind of representative of what's wrong there; it's a good scene, but you could cut it out of the movie entirely without really losing anything. I said over in the Daybreakers thread that I wish I could have taken a half hour away from this movie and given it to that one, which I saw immediately before, as they both probably would have been better for it.
Reading Devin's review after seeing the movie, I really agreed that I wanted more of the bits where you see through Holmes's eyes, though, or rather that I wanted more of the scenes we already had to be like that. The scene in the restaurant where he is initially picking up little details, perhaps making deductions about the diners around him, but is soon overwhelmed by the sensory noise because he hasn't got anything to focus on, is great, the planning of the punches is great, and those things are let down a bit by the rest of the movie being, not stupid, but more interested in flying scenery and explosions than in Holmes and Watson.
Ultimately, I had a very good time watching it, but I wouldn't bother seeing it again and it didn't spark any interest in the sequel it spent so much time promising.