So far the only sequel I liked better than the original.

Rating: 8/10 (23 November 2011)

IMDb Top 250: 60
I had some interesting bias going into Aliens. I thought Alien was a good movie (8.2) but I didn't like it too much, but I won't explain why here (I reviewed it). Also, James Cameron directs this film. I hate, HATE Avatar, was underwhelmed by T2, but did enjoy The Terminator.
I really liked Aliens.
Aliens makes its predecessor seem like an appetizer. Everything in that film existed for the more fleshed-out world of this one. The Alien's brilliant design is actually seen and used here, there's action while keeping tension, and there's a sense of plot development that didn't exist in Alien. This adds up to the best sequel ever in my opinion, and one of the best sci-fi's ever made.
57 years after Alien, Ripley is found and learns the planet has been colonized, but contact has been lost. It's strange to think that the other characters look around the same age as her, but could be her grandchildren. However once we get past that, the plot sails. Ripley, with a cast of marines, returns to discover what happened. The drop-off and discovery of the base clearly influenced one of the best levels in Halo. As said before, the film is tense, even with big guns. Once on the planet, it always feels like something is happening. No sitting around.
The acting is fitting. Weaver is her strong, female lead character, and gets some great lines. ("Then bill me!") The marines vary from charming to stupid, but have personality, unlike the cast of Alien. There are clichés, like the nervous first time boss, the black, cigar chewing sergeant, the tough Spanish girl, the dopey, big-gun carrying brute, and the smart leader played by Kyle Reese. I mean Michael Biehn. But you aren't watching Aliens as a character study.
The second the little girl was found, I thought: "Oh great a kid." I hate kids in movies like this. They're baggage. The Walking Dead, Terminator 2, and River's Edge have kids that have to be dragged around or should be punched in the face. But Aliens' girl is different, mixing adorable, innocent, and knowledgeable. One of the best uses of children in mature film.
I can think of several series that expanded in sequels- Halo and Riddick, to keep inside the genre. Halo succeeded, Riddick did not. Aliens definitely did, and did it first. Where Halo exponentially expanded lore, and Riddick... went a ridiculous direction, Aliens gives a tight, focused expansion. We see more locations, tech and creatures, and it's interesting and cool.
There are some good effects, too. Aliens has aged much better than Alien or The Terminator, even if it is a few years younger. We finally see Aliens for more than a split second, and I think the acid blood was awesomely used. In zombie movies, you ask yourself why the characters aren't infected even when covered in zombie blood. Don't worry about that in Aliens. The facehuggers moving about and the end creature are awesome looking.
Aliens has it all. Effects, creatures, action, and a plot. An essential action and sci-fi film. 8.5/10