SPOILER ALERT: Some thematic spoilers in the 4th paragraph. I also discuss some mildly spoiler-y character stuff in the 3rd paragraph, but it's nothing you couldn't find right on IMDB. Also it doesn't really matter too much because:
Alien Covenant is a mostly dull sci-fi film wrapped in CG Xenomorph skin, whose cool ideas buckle under the weight of dumb drama.
In an apparent effort to continue tarnishing the legacy of his most iconic work, Ridley Scott returns to the Alien franchise after showing the world that he probably shouldn't be doing that with Prometheus. Alien Covenant is a definite step up from Prometheus, but given what a trainwreck that movie was, that still isn't saying much. Existing in a weird place in the already-unnecessary Alien universe, Covenant is a sequel to Prometheus that also kinda retcons and reboots it, while cramming it with a lot more Alien stuff. It's an attempted course correction that's asleep at the wheel, and keeps the franchise spinning aimlessly through the vast bleakness of space.
Covenant feels like the film that Prometheus was trying to be before Damon Lindelof got his gross hands on it. It touches on a lot of similar themes, has a cast of very similar characters, doesn't tip-toe around the Xenomorph iconography, and attempts to add some lore to the mythology. Perhaps due to his advanced age, Scott seems to have forgotten exactly what made his original Alien so damn effective and scary: We knew nothing about the alien, and we cared about the characters. Almost 40 years later, here we are watching an Alien film full of dull human characters and needless explanation about something that nobody wanted explained to begin with.
Like in Prometheus, Michael Fassbender is the clear standout of the film, and is even more impressive this time around. Ridley Scott is much better at directing androids than he is at directing humans, and Fassbender's dual turn as Walter and David is genuinely compelling. Walter is pretty much an upgraded David; more subservient, more capable, but less curious. David's curiosity, given to him by his creator, was his most interesting trait, and he's still just as curious this time around. He's the thematic engine of the film, providing the film with some interesting ideas that are explored fairly competently.
But a film can't survive on theme alone, and bulk of the drama in this film is once again caused by boring human characters doing unbelievably stupid things on an important space mission. Unlike Prometheus, this actually plays into one of the themes of the film (that humans are an inferior, dying species and don't deserve to colonize the universe), and while that's nice in theory, it doesn't really make for compelling drama if we're forced to spend most of the runtime with them. The characters aren't as impressively stupid as they were in Prometheus, but they're still pretty dumb, and its their stupidity that causes most of the events in this film to go down. Once again, I find myself asking "how were these careless idiots given the job to colonize a distant planet and save humanity?" It boggles the mind and kills the drama.
This film promised way more alien porn than Prometheus, and on that front, it certainly delivers. Sadly, most of the aliens are CG-ridden creations that look bad and run around screaming in un-scary ways. Everything about the aliens is underwhelming apart from the damage they inflict, which is pretty well-done. The gore in the film is probably the most brutal it's ever been in an Alien film, and some of these moments are pretty awesome. But where's the tension?
By design, an Alien origin story is going to be a tough sell, and I don't know why Scott keeps insisting on trying. His knack for visuals is still very much there, I just wish he'd move on already. There are compelling ideas in both Prometheus and Covenant, but neither film really hits the mark for various, often overlapping reasons. If they took these two films, removed all of the Alien iconography, and smushed them both together into one David-centric film about a rambunctious android who's overly interested in creating life, you'd probably have a pretty tasty sci-fi stew going. As it is, with all the dumb human characters and lackluster Xenomorph elements, all we're left with is a bowl of mild alien blood that's barely even strong enough to eat through spaceship hull.