I saw it at the Midnight release (dying at work right now...need sleep.). Was it entertaining? Yes very much so. The action scenes were amazing. I thought Rorschach was great, and funny that he was played by Jackie Haley, the rebel from "Bad News Bears".
Now, I have not personally read the graphic novel (something I do intend on Rectifying), but I have heard the gist and understand the premise behind pretty well. What I can tell from what has been told to me though, the changes that they made to the movie only created plot holes. Also, they try to be subtle in the movie, not to reveal details, but they were so blatant that by the end no one even cared about the reveals, because they already knew what was going on. I will explain a little in the spoilers section, lol.
**SPOILER**
If Rorschach accomplished what he was intending to at the end, before Dr. Manhatten stopped him, the world results would have been the same. Whether it was Manhatten or Veidt, the world still would have pulled together, because the basis was still there for cooperation. It didn't make sense for the rest of the group to cave in, and make a Martyr out of Manhatten. As cheesy as it is, the exploding squid monster would have justified their reactions a little more.
*Jupiter's Daddy Issues*. They were so blatantly obvious with the comedian being her father, that when you are near the end of the movie, I could careless about them revealing it in a long drawn-out cutscene.
I did love the part where Veidt is talking in the lobby with all the execs and they were playing an elevator music version of "Everybody Wants to Rule the World" by Tears for Fears.