Aliens is fun but it's extremely dated imho. I mean, I love Hudson to death. But, the 80's characters don't "gel" well with the 21st century reality we live in, while Alien and Alien 3 don't suffer this age. Could have been made last year (albeit of course, with CGI) and the character interactions still would have been solid. Not to say Aliens isn't...but
The films within the Alien series have always fit in a kind of "period piece in the future", and the future is indeed quite grim. Alien alludes to socioeconomic issues, and so does Alien 3. Aliens, talks about them, albeit, in quite a liberal fashion.
I don't understand why more people haven't voted for the first, it's dripping with subtext both feminist, political, sexual, biological.
I know Aliens is a great movie, and I wish there was an option for all 3.
The fourth is something...I really don't see as canon.