I've been playing a mod for Unreal Tournament the past few days called Alien Swarm. Not only is it one of the highest-quality mods I've ever seen, but it's also the best game I've seen that captures the look and feel of the movie "Aliens".
All of the key elements are there: The standard issue guns are indistinguishable from pulse rifles, and the minigun from the marines' steadicam-mounted machine guns. Cat, one of the gunners, is a dead ringer for Vasquez. Your marines can seal doors with a miniature welder, set up automatic sentry guns, and use flamers and shotguns.
The other thing that gives a cinematic feel to this game is the pacing. Unlike the franchised Aliens and AvP games, you don't have to start out with wimpy pea-shooters and work your way up. Instead, you go in with a full squad, loaded for bear. The first few aliens that pop out and rush you are blown away with contemptuous ease. As you get deeper, they start to swarm in larger packs, and jump out from walls and ceilings. Eventually they're coming at you in all directions in a near-continuous wave, and having to pause to reload can prove fatal.
It's challenging. It's addictive. I haven't even managed to finish the first mission yet. And when you get better, you can do co-op play with other people on the 'net. And did I mention that it's free?