It all depends whether or not the Aliens have the advantage of surprise. In the beginning of the game, they appear to.
I think they entire idea of having permanent AI "story" partners is terrible in an Aliens game. The movies are full of grisly, screaming death, and frankly it makes things a bit scary.
If you had a squad of marines that weren't invincible, and would occasionally (or maybe immediately?) get killed in horrifying ways, or abducted and just dragged off during some firefight, it would be scary as hell and possibly even make you care about your comrades if they weren't dumber than sticks. This is based on the assumption you could make something like that dynamic though.
Without the death, and especially without the friendly fire or acid, where's any real threat? Space raptors, with dull claws and teeth.
I think that's what works so well in some of the multiplayer modes, plenty of non-scripted death. You can hear other marines screaming and watch their little blips disappear on the tracker at times. It's quite atmospheric, but then again, the Aliens are also actually dangerous in mp.