I agree. The best thing I can say about this is that it's just like watching the comic book.
Which is fun, except that the comic book already exists and it's great. If people want to watch a movie instead the Zack Snyder flick is fine and at least keeps it somewhat original.
It's fun enough to see, but more than anything it just feels unnecessary.
If I remember correctly he's also kind of the narrator in the book - we follow other characters as well, but Rorschach is the one taking the active role of narrating the universe through his diary entries or whatever. Makes his voice an obvious hook for a trailer.