The ending works a lot better, agreed. But most of the beginning and middle bits change the tone/framing/emphasis/etc to give the exact opposite meaning to what was originally intended. Biggest example I can think of is the opening battle between the Comedian and Ozymandias the mysterious assassin; in the graphic novel that fight is framed as a dying, bitter alcoholic well past his prime getting absolutely bodied in an unceremonious and fitting end to a despicable man. In the film, sure he loses in the end but it’s a much closer fight and he goes out in a blaze of glory, defiant to the end, quite literally a hero’s last stand. Snyder also does his best to make Rorschach look as cool as possible (while still being grungy and uncouth) instead of how he is in the graphic novel: psychotic, extremely antisocial, and borderline fascist. Again, the change to the ending was a good choice, but there were many other choices made that I personally completely disagree with