Checked it out at E3 today. I didn't wait in the huge line to play it, but I spent plenty of time watching the action. The Gearbox guys were all together on one side playing the aliens, vs. the attendees playing the marines in multiplayer.
I actually got some video on my iPad of the Gearbox guys playing, but got asked to stop recording. Apparently, they aren't ready to show that stuff yet (which explains why we haven't seen any screens or video of the alien gameplay yet), but it looked pretty damn good to me.
The aliens are played from a 3rd person view, and the view orientation always stays upright. It looks much less disorienting than the previous games were with the screen orienting to whatever surface you were on. Now you just see the 3rd person alien on the walls or ceilings. No crazy colors or fish-eye FOV either, however bright lights are super bright and blinding, pushing alien players to lurk in the dark like they should. To make up for it, the aliens get to see transparent representations of the other aliens and marines through walls. They also seem to have access to all sorts of ducts in the ceilings and walls to move from place to place in ways the marines can't. There were multiple alien types available, but they were only choosing "alien lurker" and "alien soldier", and sometimes "evolving" (kill-streak reward) to the big lumbering juggernaut aliens. The big guys seem to lose any ability to climb walls and sneak, but can run into a group of marines and tear them up if they are too close together.
I don't know how much of the single-player movies they were showing have been released, but there was plenty of cool stuff there as well. It looks like we're in for some cool story elements, picking up where Aliens left off.
Oh yeah, and they had some pretty cool displays as well. First up is the life-size powerloader vs. alien (same as the collector's edition statue, but full size) that attendees could get into and get their picture taken.
On the other side, they had what the sign proclaimed to be the original Queen prop from the 1986 movie. It has surely seen better days, and seems to have been somewhat restored (definitely repainted) since I last saw it on display back in the 80s. Portions of the tail were missing, so it was just assembled as if it were a shorter tail. I think they put funky lighting on it purposely to hide the flaws, but here's the best pics I could manage: