I enjoyed the Alien bits more. Running on walls (in fact, so often I never let go of anything and eventually forgot which way was down), eating people to rebuild your health, scuttling around as a Face Hugger, and so on... the Predator bit was the most boring, IMO.
True that, the Alien chapters were pretty bitchin'. I never mastered the "fall off the ceiling and eat the guy's head before you hit the ground" maneuver, but by God I tried. And yeah, the predator episodes were just "stroll around and school anybody who walks by with the plascaster". Though I suppose you could take it up a notch if you did the predator-style honorable thing and only used your blades and your spear to put the hurt on bugs.
But I always loved the marine chapters because they were scary as hell, and when I think Aliens, I think scary.
The first time I played the AVP2 Marine demo, I wasted a couple dozen rounds on more than one occasion because the motion tracker pinged on doors closing or opening (aside: AVP2 did the motion tracker up right). Scared the hell outta me.
~BakerMike