There ARE cases where a movie is just blown away by a bad case of CGI. As for Episode 1's cited scene (Jabba's scene), while it DID look tacky, well, the technology at the time wasn't what it is now, but come on! How can you expect someone to take VERY old roughs, completely edit out a character, then insert a new one without trouble? It's not the same as shooting a scene where you intend to insert some CGI! There's film quality first (it wasn't as good then as it is now), lights to take into account (they had to guess the positions of light sources at the time, instead of having marks), and just plain perspective troubles. Even now this scene could hardly be re-made better.
And now for my take on Alien: Alien 1 was based on the fear of the unknown Alien: Ripley was alone and unprepared to fight a very tough cookie: the alien.
Aliens: now, we enter slugfest, with a complete hive for Ripley to fight, but at least this time she has backup, weapons and a good reason to kick butt (and some frustration, too).
Alien 3 was, in my opinion, the worst of all of them: the interesting part (Ripley bearing an alien queen) isn't played on enough, and the movie sums itself up as two attemps to kill an alien and Ripley dying (her dive in the molten lead at the end alone qualifies as a BAD CGI moment: she looks absolutely fake. Seeing through the alien's eyes wasn't terribly good either).
Alien 4 (Resurrection) was intended from the start to be a dark comedy - Jeunet's specialty, and completely in line with his style in Delicatessen and City of Lost Children. Seen under that light, the movie is a success. Of course, if you were expecting the same slugfest as in 2 or the same chases you had in 3, then 4 wasn't for you.
Frankly, you had Space Horror in 1, Martian Slugfest in 2, Riddick's Mom in 3, that didn't leave much to explore for 4...
I'd like to add a movie: Daredevil. The hero's radar sense (while difficult to render visually) wasn't done terribly well.