I haven't seen the Ultimate Avengers movie yet, but I'm hoping it will prove something I've believed for a while now, that Comic book movies should be animated most of the time, with some rare forays into live action.
Take the Fantastic Four for example. There are few comics as packed with great stories as the Fantastic Four. If you just limited yourself to the first 100 issues, you have the inhumans, the Galactus saga, and a ton of other material to work with. The old Fantastic Four cartoon show took advantage of this material to great effect, producing entertaining, albeit not cutting edge, TV. The Roger Corman movie as well as the most recent disasterous attempt to bring the FF to the big screen were both 100 times more boring (and laughable) than the animated series. Or look at the Daredevil or Elektra movies. Actually, don't look. Cover your eyes and run screaming. Daredevil worked ok though in his appearances in the spiderman cartoon series.
There is the potential to blend things in a successful way. I actually liked the Hulk movie formally in the way that it brought together computer animation and live action. But even there, did we need the people? Why not have it all be computer generated?
The Spiderman, Superman, and X-Men movie franchises all seem like great examples of how live action comic books could work. However, just think for a moment what could have been produced if you took the same budget those movies had and did them as animated projects instead?