Some people dont like it because of the slower pace, and the human drama aspect of it. some people just want a shit load of aliens running around killng things. Weve got Aliens, Alien Resurrection and the AVP films for that if thats your thing.
Alien 3 is like marmite thought isnt it. You either bloody love it (I do) or you just dont get it at all and you find it boring. I like every single Alien, Predator and AVP movie apart from Requiem. But even that i can sit and watch (although the Predalien f**king up the life cycle always requires a facepalm) and just enjoy the carnage (from what i can see, because its so irritatingly dark).
I also dont mind AR. It starts so well, and you can see that it could have been brilliant. But it completely loses its way in the final third of the movie and the ending is a mess, ruining the whole thing. But its still enjoyable to watch.
Nothing will touch the original Alien Trilogy and the two Predator movies though. Although Predators is looking very promising