Alien Resurrection is better than Alien3, but still has a weak plot and characters. Its action's good; it has more in common with disaster films like Deep Blue Sea, so despite its failure as an Alien sequel it works on its own terms. If you want a simple gory thriller Resurrection delivers.
200 years after Alien3 scientists at a military outpost clone Ripley from a blood sample so they can extract an alien from her. If you've seen Alien3 you'll wonder how and why they did this (and why if they were going to it took them 200 years) but they did, so now Ripley's back, I think. I'm not sure if it's really the same Ripley from before. Whatever. The filmmakers needed Sigourney Weaver to draw fans in, I guess, so this is their reason. There's also some mercenaries, including Winona Ryder and Ron Perlman. I like Ryder as an actress, and though she isn't challenged here I think she does well. I'm also a big fan of Weaver, who in a way helps save this material; another lead might have pushed it further into mediocrity. Her and Ryder have a few bonding scenes, which is an Alien staple; there's always one character to soften Ripley, from her cat in Alien to Newt and Charles Dance in the sequels. It isn't exactly compelling this time, but it's handled better than in Alien3.
The most amusing performance, however, is Brad Dourif's as a weirdo scientist. Dourif is a bit like Christopher Walken: you don't know why he's here, but he's so entertaining that you don't care.
This is probably the goriest Alien film. Some of the deaths are nicely creative and gross, even if very contrived. There's quite a lot of blood and goo. That said, this film shares one of Alien3's problems: the aliens don't have much personality. Resurrection establishes them as intelligent, but unlike in the first two films they don't seem sly or predatory. They behave like sharks or slashers, sneaking up on characters when the plot requires them too, but otherwise not serving much purpose.
For fans of the series Alien Resurrection is worth getting, however, and if you like gory thrillers this one will do. Just don't expect the spark of genius which drove Alien and Aliens.