First of all, for those of you who haven't read or finished the book, READ IT. And read it slowly. There is a lot in the book. It is not your average superhero comic. It's hardly what you expect. Don't expect many action scenes either. Watchmen is a deconstruction of the superhero genre. In fact, the only person with superpowers at all is Dr. Manhattan (the blue man). There are many themes in Watchmen. If you're reading it and thinking "this book is alright," you're clearly not understanding the subtext. Watchmen is the only graphic novel to be on Time's 100 Greatest Novels of All Time list, and to win the Harvey Award. Zack Snyder is working hard to make this movie as close to the book as possible, he really understands the importance in this.
Having this said, I can understand if you haven't read the book and weren't impressed with the trailer. The trailer was really only designed for the fans of the book. Joe Shmo's trailer will be out closer to the release date.
I don't mean to come off as an intellectual snob here, but this isn't just some average movie sequel or chick sci-fi movie here. It's Watchmen. This is important. Read the book. And think hard about it.
Edit:
As for my opinion on the trailer? It blew me away. I'm heavily looking forward to this. It might be better than The Dark Knight, and I love that movie. The music? Ironically perfect. It fits the atmosphere nicely. I read somewhere that they wrote it with the 1939 Bat-Man in mind, even if it was for Batman & Robin.