The comic was a masterpiece. And this adaptation is...a HUGE missed opportunity but at the same time (given such a terrible track record) the best we could have hoped for from Hollywood on Watchmen.
The biggest problem IMHO is that, as one reviewer put it: "[Zack] Snyder's Watchmen is mechanical, heartless and, tragically, hollow." Also Snyder took a HBO-type of drama and made it a ridiculous action flick (and I'm somebody that grew up loving action flicks). And no, I didn't care for the changed ending from Moore's super pulpy original ending. Also, I personally didn't care for Matthew Goode's Ozymandias.
(300 was a great example of Snyder doing adaptation right (with perhaps material more suited to his innate sensibilities) vs Watchmen which he was ill-suited for except for his superficial respect for its visual aesthetic)