I find it hard to compare AvP with A:CM just because AvP happens to have marines and xenos in it. What makes AvP unique is that you get to play all three different species, all pitted against one another. It may be too early to tell, but if/when people start playing better-organized games online, then AvP could rock on for a good long time and be even more fun than it already is. If not, I expect people will eventually tire of unorganized free-for-alls and death matches that offer no real strategic challenges and little long term replay value.
On the other hand, in A:CM you have the Colonial Marines from "Aliens", the "ultimate badasses" going up against an unknown alien species... as far as they know, it's just another bug hunt. Something like a sequel to "Aliens" might have been. This should be a perfect format for well-organized multiplayer coop games where you really need to work together with and depend on your fellow squad members. While that style of play may not appeal to everyone, I think it would set A:CM apart from most other combat action games people are bound to compare it to. In AvP only the "Survivor" match offers genuine co-op play for the Marines, while this is an entire game dedicated to playing as a Colonial Marine, so I would expect quite a bit more depth to any co-op/multiplayer combat scenarios in A:CM.
Of course it all depends on what kind of game Gearbox is actually making, but I suppose most fans of Aliens and gamers alike are really hoping for a gaming experience that combines the best of modern combat games with one of the most popular movie franchises there has ever been, and that it turns out to be a perfect marriage of the two. That's what I'm looking forward to anyway.
