I saw the Alien franchise for the first time about a couple months ago. I have not seen Resurrection (more like a few scenes to know I don’t care to see it) nor the AvP one’s. Prometheus, I saw parts of this film before seeing Alien/s/3 but it has been awhile so I don’t really know how to judge Prometheus until I actually watch it from beginning to end.
That said:

Alien 9/10
This film really surprised me. Prior to viewing, I had this mindset and expectation that Alien was only liked because it had a cool looking alien and had the appeal of a horror story set in space with cheesiness and bad so-so characters. Instead, I was blown away how timeless it looked for a film in 1979. Other than the dated computers, everything looks really nice and believable. So on visual terms, it works. Character and story wise, it is done justice. How the characters interact just flows so well and sets up tension through their little disputes. The story is a nice thriller with bits of mystery and imagination left to the viewer. It never bores me. Instant and well-deserved classic.
Alien³ 6.5/10
After coming off Aliens, which I’ll get into later, I was glad it was closer to Alien in terms of tone and atmosphere. The crazy thing is that I was more interested in these characters, especially Charles Dance’s character, but damn, I don’t think they gave him the justice he deserved. While Aliens was excessive in bringing in new characters, not that Alien³ didn’t too, this film was too excessive in respect to killing off characters. Like okay, you’re going to off a couple of characters from Aliens so that you can work off a ‘clean slate’, but then you’re going to add insult to injury and kill off one of your own interesting new character. I get thematically, this film has that theme about “Death”, but it doesn’t work well if it’s used in excess, in respect to what I described earlier. There’s list of other issues, obviously the horrible puppet work on the alien comes to mind, but overall, I liked most the dialogue and most of the characters here. If I had to watch a sequel in this franchise, this would be it.
Aliens 5/10
Very underwhelmed with the product given here. As soon as the space Marines are on-camera, that’s when I started to think… something’s off here. Unlike Alien, this film looks and feels dated in all the bad ways. One-liner comedy and guns a blazing. Some say the effects really hold up, and while Alien had a few minor effects that didn’t age well, Aliens overall look and feel doesn’t hold up for me. One scene that comes to mind is when one of the drop ships crashes, and it’s like, I can tell it’s a background projected behind the actors. It’s not horrendous, and definitely not on the levels of Alien³ puppetry, but considering how well crafted and solid the first film was, this was a let down. Aliens is also a huge disappointment to me because it really feels like a blatant remake or retread of the previous film. Alien³ is not innocent either, but I’ll give it props for being a lot more creative than the shoot everything that moves route as well as how bland the story unfolds beat for beat from the first film. If a sequel to Alien had to be done, which inherently, I didn’t really think Alien needed a sequel, but if it had to happen, I think it should ideally flesh out and explore Weyland’s motive behind wanting the “Perfect Organism” so bad. Obviously, they want to use it as a weapon, but against who or what? How did they hope to use it? Alongside this narrative would have Ripley trying to sabotage and taking the fight to Weyland. Sadly, Aliens and Alien³ aren’t that impressive to me since each sequel more or less copies the story of Alien and less so of expanding the story.

From the little I know of Prometheus, and knowing how Ridley Scott wants to create five or six damn prequel movies, I can’t say I’m thrilled about that either. Alien itself was a solid film and everything else feels derivative.