How watching Watchmen might turn into a depressing experience:
1. Either you’ve read the extraordinary comic and you won’t recognize it.
Gone are: a carefully revealing puzzle, everyday hero backgrounds, their naive intentions, the retro-graphics, the suggestion of violence.
Enter: explicit atrocity, underportrayed characters, übershiny costumes and graphics. Luckily the end scenes preserve the philosophical core of the book and (just partly) save some of the movie.
2. Either you haven’t read the extraordinary comic and you have doubts.
You wonder: what is this movie about? What connects all pieces?
One advise: read the book. Reconsider this obnoxious movie afterwards.
By the way, it is NOT impossible to make a good movie from an Alan Moore product. Check out V for Vendetta (soundtrack by David J). And while From Hell may have been mediocre, Watchmen is really disappointing.