I love the first one as a proper horror film, and love the second one as a great action film. Alien 3 always seemed to stand well with the other two by returning to the horror genre, and expanding on Ripley.
In the third film, Ripley has lost everything that she fought so hard for in second film, and it’s her against this alien that has taken everything and she knows it’s finally going to take her life in total.
The setting in Alien 3 was very original as a penal colony that’s just hot and dark, and the design of the alien is entirely different since it burst from a dog (or, a bull if you watch the Director’s Cut). The alien moves faster and more haphazardly and the cinematography reflects this as well. The final scene with Ripley’s sacrifice is the fitting end to what was a trilogy at that point.
I don’t know whether people confuse Alien 3 with the 4th one or what, but Alien 3 is a fantastic film that holds up well decades later. I’m always confused by the fact that people slam it so often, and it wasn’t until I saw people crapping on it online that I realized that there was even a consensus that it was bad.