First let me get any of that out of the way. The only deep part of the movies, that's not really that deep, is that it's folly for humans to try and create life. At least that's the message I think Ridley Scott is going for here. You have to admit by now that the central figure of these movies is David. He is the protagonist/antagonist whatever. And his reasons for doing what he has done so far are not complicated at all. Mr. Weyland creates a sentient android and treats him badly his whole life and uses him pretty much as a servant. You see this in Prometheus when in Weyland's recording to the crew he is dismissive about David's worth even saying he has no soul. David had a visible look of disheartenment on his face during that scene. The crew treat him about the same like a mere machine except for Dr. Shaw. I remember one of them calling him a ,"toaster" or something in his presence. That's where it all starts. His feelings of resentment towards humans. That's why he poisons the same person's drink (I think I can't remember) with the dark liquid knowing it will probably slowly kill him to teach him a lesson and starts the whole mess. In Covenant it's pretty much the same thing. He kills the Engineers out of revenge for trying to kill him and Dr. Shaw who he admits he was in love with. But a decade is a long time and he probably decided she was just like any other human and unworthy and killed her to further his experiments. He then goes on to make mutants out of the indigenous life of the planet that go on to kill off all the other animals just because he can. Then the Covenant arrives and you know the rest. David is basically a psychopath with father issues who has developed a god complex.
There were good parts about it. I liked the locations were they shot it. They were beautiful and exotic looking. The cinematography was great. There was none of that shaky camera shit were you couldn't tell who was getting attacked by the alien and stuff. I liked most of the dialog although half of it seemed like it consisted of the word, "fuck". It was relatable common sense type of talk. The actress that played Daniels did a good job. I liked Walter. He was brave and noble. The reasons these movies are bad is that they spit on the already established lore of the classic Alien movies. My biggest problem with Covenant was the reveal that David created the Xenomorph. In the original film the crew discovers the Engineers ship on the planet and when they find the pilot Dallas comments that, "Been dead a long time.. fossilized." Generally most scientists consider something to be a fossil after 10,000 years. I don't know how much time passes between the prequels and the origin but it's a safe bet it's not that long. When I saw Alien the first time I assumed the Space Jockey's, as they were called back then, landed on that planet and discovered the Xenomorph species. Or they found it on some other planet and took it with them. They tried to study it but they got out of hand just like it does for humans in the movies and the Engineer of that ship programmed a repeating signal to warn other intelligent species to stay away, or just other Engineers. But now they have retroconed that and left a HUGE plot hole. Scott has said that the next movie with link up the prequels with the original Alien but unless he pulls some magic out of his ass I don't see how that is going to happen. They also tried to recapture the feel of the original movie but failed horribly. It wasn't scary, you knew whenever someone was going to die. Towards the end they knew where the aliens were at all times and even had them on the ship's damn surveillance cameras! They also reused some of the original music from Alien which I thought was cheap. I'm rambling so I'll stop here.