I had the same exact experience as mouser. I occasionally read the occasional comic book as a child, was never too into them. Superman, Batman, etc. When Kingdom Come came out, I was mesmerized. Comic books tend to have stupid stories normally (they're for kids, right?) but Kingdom Come was a good, adult story with that painted art, which was cool and different. Then I got back into graphic novels for a while. Then, the stories started getting really ridiculous and unnecessarily complex like Universe X, PAradise X, all that stuff. But I still enjoy them once in a while. I love the art and the stories are good enough. Some of the more interesting ones that I can remember:
--Marvels (similar to Kingdom Come)
--Paradise X, Earth X, Universe X
--Batman: The Long Halloween, Dark Victory (one of my favorites of all time)
--Wolverine Beginnings (or something like that)
--Any of the Ultimate stuff is kind of cool
Of course, Watchmen was one of the best I've read also. They actually used it in literary courses at Berkeley.
The thing that gets to me about comic books is that they try to explain all the fantastic stuff that is happening, and it ends up becoming just a little too much. THings like parallel universes, gods, superheros, genetic stuff...it can all go crazy quickly. Usually, I like an easy to understand story with some good action and good art. Not to kiddie, but not too geeky or quirky either. I view comic books like action movies...I want a nice, rated R story, but I want to have some fun, not think too much.