Watchmen or dark night?

As most of you know, there were two superhero films that came out in between 2008-2009, those two movies were The Dark Knight and Watchmen (not including Wolverine). There is one thing that's been puzzling me for a while, everyone in the world of movie reviews have said that The Dark Knight was a really, really good movie, in my opinion i would say that i only liked it because of Heath Ledger and his role as the Joker. But why didn't all the critic's say good things about Watchmen. The only thing i didn't like in that movie was the way they changed the ending, other than that the movie got most of the novels story, events that happened in the book, characters, and what the characters say even the small things they say which were pretty close to the graphic novel (which is my number one favorite book of all time). So my question is, why aren't they acknowledging a novel based movie which has good characters and a complex story line that goes well when you put the chapters and characters together, and instead the reviewers and critics are acknowledging a movie that is based on a cartoon that you can watch on WB kids? It just doesn't make any sense.