I think people are harsh towards Alien 3&4 and the prequels. The 3 and 4 were good movies in my book, just not on the goat contender level for horror and action movie the first two were.
The 3 had that wicked and claustrophobic apocalyptic ambiance wich suited well the whole "we are trapped in a prison facility in a prison planet with no guns and an invulnerable man-eating predator" situation and did a good work on the evolution of Ripley's character. Plus a dog alien that runs like hell and was well done in CGI for the time.
The 4 had some cool ass space pirates, good looking aliens and delve a bit more on the darker side of Ripley, big tech companies, the android question (that have been a continuous topic since the 1) and horrific-sexual stuff that also was on the first then forgetten (after all we are talking about humanoid predators that like to put their tails between women's legs and are born from a mouthraping gagging double hand creature itself born from a pussy-cross egg). Too bad Jeunet is anything but an action real.
Prometheus & Covenant are underrated too IMO. They considerably expend the lore and are full on big SF movies, wich I like, and don't get stubbornely stucked on the Alien itself. One more time, the big tech companies, the androids, ethics about creating / preserving / killing, a bit of the sex-horror stuff are interesting thematics that were present in the original and developped in them. Prometheus obviously went a bit in all directions but Covenant actually did a good job of thightening the storie and providing explanations. And had the balls to have a bad guy winning, dark and grim ending.
Plot holes, mysteries and stupid human behavior were all present in the first one without people getting all riled up anyway. I mean there was no explanation whatsoever about the space jockey, the crashed ship or the company knowing about that unknow specie on an unknow planet. Or wtf was the alien doing chilling between tubes in the final sequence as it is about to be thrown in space while the whole movie it killed every human crossed in seconds. And we had a guy putting his head the closest possible to an enormous alien egg hatching live and two different characters on two different occasions searching for a fucking cat, unarmed, alone while people are getting slaughtered left and right...
I think people just tend to be more entitled and less imaginative today.
On a sidenote, that shitty ugly human-alien hybrid and all the AVP of the world can suck my dick.