As someone who disliked Scott Pilgrim, realized that I was supposed to dislike Scott Pilgrim (the character), and then liked Scott Pilgrim a lot, I was very excited for the film. Michael Cera is perfect for the part (the casting is perfect), the style worked great, and the music was pretty good too. The problem comes through with the adaptation to the screen.
The movie is a little bit shy of two hours, with the majority of the movie being ridiculous fight scenes, musical numbers, and one-liners. This is problem number one, because the source material is six rather thick graphic novels chock-full of dialog and exposition. Seven evil exes is a lot to cover in an hour and 45 minutes (roughly 15 minutes per ex). This doesn't leave a lot of room for the emotional content of Scott Pilgrim that made it really appeal to me. Sure it's flashy and kung-fu and "an epic of epic epicness" but it lacks the power of heart that made it so great to read.
The movie does a poor job on Scott's backstory, and by poor I mean that it's barely covered. Scott and Kim's relationship is barely touched, so when Scott apologizes to her I found myself wondering, "what for?" Envy Adams has an incredibly small role, only appearing during with the third evil ex, and her relationship with Scott is immediately forgotten. It builds it up and then drops it to go to a very long fight scene (like ten-ish minutes). Yes, it was cool to look at, but the stylized bass battle takes away from any sort of maturity that Scott could get to (such as legitimate closure with Envy).
Also, the ending (SPOILER ALERT) is kinda weak. It resolves rather hurriedly, and Scott really doesn't learn or grow like he should have. Gideon is not the ASSHOLE, and Scott never really confronts himself (He makes peace with the negaScott, but doesn't except his faults as well). It just sort of cops out and hopes that a happy ending and swordfights will cover for a copout.
These are the complaints of someone who wanted to see a movie of the book. I know that's not possible. This is more mass market appeal and that's great. I'm glad the book got publicity but the movie lacks the power to actually make any sort of statement. Maybe it should have been two movies, or maybe they should have toned down the LOOK WE'RE NERDY LIKE YOU and KUNG FU. Maybe they should have let the graph finish before they wrote the movie.
In short, it's really fun. If you were a big fan of the books you'll be a bit disappointed. I enjoyed it, but I found myself wanting more dialog and less style. Plot is good. That's why the books were popular. Add a little more of that next time and we'll be good.
(I wanted to avoid a rant here, but there is a lot missing from the books and some serious changes that don't really work. I'm not going to list them, just be re-warned)