I only saw Alien relatively recently. It was on my list of must-sees for a long time, but for whatever reason I never got around to it.
The first film is a masterpiece of the sci-fi genre. The sequel seems to be beloved as well, but I find the shift to straight-up action a bit jarring. I’m sure with repeated viewings I’ll love it too, but it was not what I was expecting. It has a very Rambo: First Blood, Part II feel to it.
The latter entries are less connected, but they successfully introduce cool ideas and have plenty of fun. I like them more than most people do, I think. I have not seen the Ridley Scott prequels, but I’ll add them here when I do.