It was a decent enough game, but if it'd just been exclusively Marine, wouldn't have had the replayability factor. Having recently reinstalled it, I'm remembering how fun it could be. Mostly, when stalking someone unaware as an Alien or Predator.
That's when the multiplayer games were at their most fun... When it was just a handful of people and it turned into a hunting situation. The more people there were, the more it graduated into being a messy clusterf**k, like with most games.
Marine part was definitely too dark for you to keep being sent into it on your own, though. Needed at least one other with you, because you felt less like a Marine and more like just some random dude who'd managed to pick up a gun.