I started playing it last night.
The story is excellent so far. You start in a USCM ship that has answered Hicks' distress call, so it basically picks up right after the film Aliens. Which I thought was a brilliant idea.
I like the weapons and how you can upgrade and customize them as you go.
I absolutely love the aliens. The movement is extremely lifelike. I still panic a little when they attack, as they are so slippery and fast, and can climb on anything. The AI is pretty good as well. They will run away if they feel they're getting their arses kicked.
The atmosphere and scenery are very good as well.
My only problem with the game, so far, is the actual graphics and motions of the marines themselves. In this time and age, I'd expect maximum realism, on this front at least. Black Ops and MoH character graphics are far superior, IMO.
Nevertheless, as a fan, I'm thoroughly enjoying it. You get to revisit the colony and be in similar situations as Hudson and company. I love how you can find their weapons lying around, in the same places where they died or dropped them in the film.