Original Alien is one of the best science fiction movies. I don't know what you call about "bad characters" - it is litteraly story about rusty space truck with some team of very ordinary people. All dialogues and conversations feels real and natural from how generaly they talk and act - not like actors who play, but like real people - most of which not very smart. I think scene of dinner before the birth is mine favorite in this regard. Characters can't change ir evolve or show us their "deep iternal world" since overall event is too short, but we given enough background to belive that they are not background but actual people, characters - and there kind of too much of them, but this works, and works better than it "The Thing" for example, althrought "The Thing" is exellent movie too.
Combination of characters based on real, averege people, rusty-dirty science fiction but very belivable enivorment created pure opposite to fairy-tale of classic clean and heroic science fiction. Because this movie feels very real - this is not starship enterprise with cardboad bright walls - no, you can feel everything, get into situation very seriously, and add to that realism to got this horrific dark technological maze as claustraphobic place, blackness of space around and one of the most strongest ambient soundtrack ever made. And all parts of movie works on this single idea of complex psyhological horror that tell absoluetly science-fictiony story, but same time feels as real, as possible.
Third movie problem... well at first it was mean to be set in millions years in future where monks flyung on spherical wooden ships - this I'd watch lol. But well, how it ended it was nice too. I clearly get what director aimed it and multiple times watched regular and director's cut version. But oh boy director's cut version is long and a lot of this scenes is pointless - and this is problem of movie. It trying to build concretic atmosphere, but most of this elements don't really needed and same time I feel like something missing from film to complete this overall picture. Feel of prison also in places felt unnatural - yes, director kind of wated to shift to emotional aspect - and while he sucseeded in some places... in other eeh. Mine favorite parts of movie is again awesome ambient soundtrack, scenes with storm over Fury 151, also ending - I absoluetly love desighn of soldiers and people from corporation. He trying hard to make something unusual, something in concretic style of no-so-generoc future instead of 2nd movie "u.s.of.a. marines in spess" and I feel sad that we don't get more of it instead.
4th movie was directed by french director as I know and you clearly see it from a start. It trying to build your science fiction world and give back to it instead of just making some situation with abstract background, so you need tune up into mood to expect parts that may remind you fifth element, Jodarovsky's comic books, Riddic movies. Stylish rustiy future that gone too future, so in places it feels like fantasy and already go into "warhammer" category of future. And it feels really great - I'd not call this movie "dumb", it just gave some crazy scenes and world and you got what you need to expect, but it is also "universe" you want more stories in.
Promwtheus... err, this movie don't have any real "deepnes" like it trying to show and besides it there not much really complex - exept maybe some "black goo + vore" fetish but in rest it not very complex science fiction movie with pseudo-philosophical background "oh what if we was created by ayyliens and we will find this ayyliens?" and some scenes in it as you know not very smart. Covenant already have a lot really idiotic scenes, almost modern disney tier plot elements mixed with even more amounts of pointless pseudo philosopy and movie trying to sell it by "nostalgia" on original alien. Pathetic, this movie remind me Terminator Genesis. I'd rather than this 2 last movies better take Alien vs. Predator movies and vidja games, thanks.