Everything I'm going to say here (apart from my last line I would guess) has been said to death already about this:
Yes, if you've got A.D.D. you'll struggle in the slow bits; Yes, Malin Akerman lets the side down a little bit; Yes, Jackie Earle Haley nails it (which turned out to be a bit of a fluke); Yes, the changed ending is actually pretty good; Yes, although they removed of several layers of complicated comic-book structure, what was there felt like it needs more time; Yes the choice of 'Hallelujah' for the 'love scene' is just absolutely fucking horrific (and some of the other music is questionable too) and God yes, Zack, please leave the slo-mo button alone.
All that being said, I'm one happy fanboy. Cinema is a obviously a different medium so compromises and changes were inevitable, pointless being precious about it. What is here looks and feels pretty good, the edits and changes are mainly well judged and, considering the reverence with which the graphic novel is held, it works very well (and could easily have been so much worse).

To sum up: Fans of 'Hallelujah' and dangling blue cock will think this is the best film ever made.