As far as licensed lames go: It's so okay it's average.
I'm gonna say I was one of the people really hyped up for this game, and I even rewatched Aliens in anticipation. However, when it got mixed to negative reviews, I decided to hold off buying it and rent it from Redbox instead. Here are my thoughts.
The Aliens are fun to shoot. They come in a large variety of types and you'll feel a total badass when you mow 'em down. At many points, they were scary, too, which is even better.
The story is okay for the most part (some weird bits are in the "Bad" section). The characters are likeable enough for me to care about them.
The weapons are AWESOME. All the movie weapons sound authentic, and there's a whole bunch of other weapons too. What's more, they're all customizable, too. Finally, unlike many other games, you can carry all of them, so no need to worry about missing out on your favorite gun (for the most part anyways).
There's a lot of attention to detail. Everything is modeled as closely to the movie as possible, and there are character weapons lying around, as well. Ever wanted to run around with Hick's shotgun, Hudson's Pulse Rifle, and Vasquez's Smart Gun? Well, you can!
Why does Keyes blow himself up? As the entry in YMMV explained, it makes no sense whatsoever.
Why can't I use the Smart Gun whenever I want? It's my FAVORITE weapon in the entire franchise, is it's only in it for two levels, and one of them is a secret you have to find.
The graphics look like ass. The textures are constantly popping in, and the general look of it looks barely better than Doom 3, which came out nearly 9 years ago.
There's a TON of bugs. as none of the months it got delayed used for bug testing? There's clipping, AI issues, occasional gamebreaking bugs that require a reset etc. Hopefully these get patched later, but jeez.
The human enemies are NOT fun to shoot. I play an Aliens game to shoot XENOS, not humans. Also, these guys have impeccable accuracy, unless you have Hudson's Pulse Rifle, they're also frustrating to kill. If you get close, you're dead. Easily the worst part.
I generally liked it. It's better than most licensed games, that for sure. However, if you were looking an uber awesome game starring your favorite alien, you'll be disappointed. It's serviceable for nostalgia, but it's not the Aliens game we waited 6 years for.