Both Prometheus and Covenant are great. They're actually pretty cool Alien "prequels".
That's also why there are so many garbage opinions on the first page of this thread. I guess, it's because these people are die-hard "Aliens" fans - you know the one with a lot of a action, a easily to follow story and lots of shooting.
Prometheus and Covenant are 2 prequels of a planned 3 or 4 prequel movie series. Prometheus has some flaws, but they have been waaaay overblown buy a group of certain haters, who got offened by its supposed "confusing" story and certain ways certain characters behave (yet, easily to neglect in the grand sheme of the story).
Prometheus is not for the Alien action crowd, it's for the people who appreciate (and understand) the deeper parts of the Alien lore, or like thought provoking movies in general.
And Covenant? Covenant is absolutely fucking awesome. Minor flaws, yes, but there are so many cool Alien lore references in there - its awesome. It's a love letter to the original HR Giger design (all the parts with Shaw). It also explains the behavioral nature of the "aliens", which were often seen as "just animals who want to survive". Nope. Covenant shows us aliens who are way more intrinsically "evil" and/or unnaturally aggressive (it makes sense, if we understand what they they really are).
Also, Fassbender's character David alone, and everything that encompasses his story, makes this movie an 8/10. The ending is fucking great as well.
Overall, I'm very pleased with how these 2 Alien "prequels" turned out. True alien fans learned a lot about Weyland Yutani, The "Space Jockeys", Androids, the origin of the Aliens, the Aliens themselves (and face huggers), while still offering enough "mystery" to keep the brighter ones thinking and talking about the movie.
Fuck the haters!