Didn't see a thread for this movie so I thought I would post some impressions after seeing it today with my brother.
In terms of plot (what little there is) Alice continues her fight against the minions of the Umbrella Corporation and the endless zombie horde. This time around Alice and her friends are fighting to escape a gigantic testing complex located in the former USSR (think the Star Trek TNG holodecks with the safety protocols turned off) where they meet good and evil clones of former companions and enemies. You don't see a movie like this for plot; you go for the action and check your brain at the door. On that level the film delivers with some well staged action sequences, even if many of them feel like riffs on similar setpieces from other movies. Late in the film for example, Retribution goes all Aliens as Alice must rescue a little girl who may or may not be her daughter; the whole sequence plays out like the Ripley rescues Newt section of Aliens, right down to the girl stuck in a gooey pod. And of course, the movie ends with yet another quasi-cliffhanger. Still on the whole, I was entertained.
In terms of 3D, the film looked to be shot natively and has a very strong sense of depth for just about all its running time; there is also lots in the way of bullets, shrapnel, blood and all sorts of particles that fly out of the screen towards you (more than the prior film, I thought). In particular, a chase sequence around a reconstruction of the Kremlin as our heroes are pursued by zombified USSR soldiers armed with everything from machine guns to RPGs was especially entertaining and both made me duck a few times and wonder what one of those classic Bond chases would have looked like if it had been shot in 3D (not that the current filmmakers would ever consider doing something fun like that again in one of their now turgid movies).
If you liked the previous Resident Evil movies then you'll probably like this one as well; just don't go in expecting thoughtful plots or characterizations, as that's not what this series is about.