I really enjoyed the first one, though I did find myself not paying attention at some points, but that was by no fault of the movie (I think). I recall being really out of it that day. I watched it a second time and was pleased at what filled the blanks in my memory.
I'm excited about the second one because we get Moriarty.

I'm really hoping this will continue as a movie series so we can get more of the Holmes stories on the big screen with Robert Downey Jr. because I really doubt they're going to find anyone better than him for a loooong time (and because I'd like to see their interpretations of the other stories ^.^).
My major irritation with the second one right now is the trailer. I have eyes that are super sensitive to light (I have big pupils), so all those white flashes actually cause me physical pain. :/ If it wasn't Sherlock Holmes, I would probably refuse to see the movie on the merit of "If you have to flash really bright screens in your trailer in order to make it seem edgy and exciting, then you're jerks that don't care about anyone and can't make a trailer that doesn't rely on blinding your audience." But being what it is, I'm going to have to make the exception. XD