The campaign was so so. It seemed very slow and and tedious, not to mention the unbalanced system of the shove with the marine. Damage output was notable, and movement lag was often, even when playing offline. The multiplayer was fair. Reminded me a lot of Left 4 Dead, with the Lurker acting as a hunter. Lag was rare but many glitches were accessible and the wall climbing ability was difficult to control. The damage between the marines and the aliens was unbalanced, giving the aliens, not only an advantage, but a guaranteed win in most situations. Overall, could have been better.
I didn't believe the hype or negative reviews and had to see A:CM for myself.
I've played probably every Aliens game that has come out in the past 3 decades (I'm 30 years old, I've been around the gamer block a few times). Even if you are a big Aliens fan like myself and WANTED this game to be good, there is nothing remotely good about A:CM.
I know what you are thinking "It can't be that bad"... because that's what I thought. My expectations were low to begin when I rented it. I have to say, every bad review is absolutely true... and anyone telling you otherwise is either blinded by their love for Aliens OR they haven't played it yet. I won't go into specific details about why it's awful, because frankly the game just fails in every possible category.
If that doesn't dissuade you... you might also note that Timegate (co-developer) is filing for bankruptcy after helping make this game. That speaks volumes for the quality you can expect.
Don't rent it... don't buy it. Just don't. Forget this game ever existed.