I've come to the conclusion that I don't like the Ultimates.
The characters are mostly static and interchangeable. Their most definining characteristics are their pasted-on faults. Iron Man's an acholic, Giant-Man's a wife beater, etc. None of these character flaws are ever looked into in depth, or resolved/dealt with. It's taken the best of Stan Lee's basic premise of all Marvel comics (Superheroes with Human problems) and caricaturized them into ridiculousness. In 12 issues or so, I don't care any more or any less about any of the characters. Captain America could get shot in the face, and it wouldn't affect me as a reader. Any emotion behind the characters are as pasted-on as their flaws. It's all just translucent skin.
The wait between issues doesn't help. Planetary didn't come out for something like 2 years, and when a new issue came out, I was still as involved with it as I was when it was initially a monthly book. I cared about the characters, situations, etc. Ultimates doesn't have that.
It also doesn't help that little to nothing happens in any issue. It took four issues to build to the Ultimates being "blown up" and revealed to have escaped off panel with a tidy and ultra convenient explanation, for 20 more pages of really nothing going on at all.
Overall, I don't give two shits about the characters, the wait between issues isn't worth it, and the fact that it takes six issues for one thing to happen wrap into a big pile of crap.
Millar, when he wants to be, is a fine writer. Swamp Thing, Superman Red Son, the first two arcs of his Authority run, all prove that to me. But so far his Marvel work has been barrel scrapin' craptacularness. I am looking forward to his upcoming non-Marvel work.