Alan Moore must have taken his name off Watchmen out of jealousy. It is a beautiful and very faithful rednition of the comic book. The ending, while substantially the same thematically and plot-wise, has a significant change to the specifics of the villain’s plot that makes it, if anything, more plausible and satisfying than the original.
The action is brutal, the effects spectacular, and the characters as layered and complex as the ones that made the book a classic. You should probably go see it immediately, in IMAX if possible.