With so much interference from the studio honchos and a constant scratching of script ideas, it's a miracle they were able to end up with a product which was
more or less very faithful to the original saga's timeline.
Let's admit it, Scott made a masterpiece (IMO, anyway) and Cameron upped it by a big notch. It would have taken pretty big (and really strong) shoes to follow those two's steps, and that too with full freedom guaranteed by the studio. The only person I think who could have made a mind-blowing 3rd Part was Sergio Leone, if only he ventured into such films.
Fincher did his best with what he had.
I downloaded a bunch of all the proposed Alien 3 scripts and the best one I read was the one where Ripley gets kidnapped by the aliens while still in her hypersleep, and Hicks and Newt come out of it prematurely to find out Ripley was missing, and follow her tracks to the aliens' Planet (more like a breeding ground) to rescue her. There they come across a new and extremely fierce species - Navigators (the huge dead fossil encountered by Dallas, Kane & Lambert inside the derelict spaceship in Scott's Alien), who are much more aggressive and deadly, and use the aliens borne by captured alien Queens for their own death games across the universe.
Imagine what a killer Alien 3 that would have been!
EDIT - btw FC, this is for you -
http://time.absoluteavp.com/time1.html
Enjoy. :)