From HuDaFuk (Xenopedia editor) -
Overall, I liked this more than Prometheus, but it had definite faults.
It was undeniably a more commercial, less ambitious movie than Prometheus, but I thought that ultimately worked in its favour. There were a few hints of some of the higher concepts of the kind explored in the previous film, chiefly in the scenes involving David, but on the whole it was a more straightforward film. More action-packed, more intense. I'm also happy to say it fixed one of my biggest criticisms from Prometheus - whereas the crew in that were terribly cardboard and uncharismatic, I'm pleased to say the characters in this immediately came across as more interesting and likeable to watch.
However - and this was my main problem - it was one of those movies that suffers quite badly from a case of deterioration; it seemed to get less impressive as it went along, culminating in a final act that I thought was, disappointingly, pretty weak. The Neomorph birth sequence, seen in the previews, was excellent and probably the best part of the movie. But towards the end, more and more things started happening that really disappointed me.
Spoiler
For instance, they once again messed with the details and timescale of the Alien reproductive cycle. Crudup's character is infected and gives birth in about ten minutes, whereas later in the film someone is impregnated after a Facehugger is in contact with them for no longer than a few seconds. Seriously, they're never even knocked unconscious before the thing is cut off them, and yet they're still infected. Also, for some reason the Chestburster is now a fully-formed, miniature version of the Alien, with arms, legs and head, rather than the slug-like design from the previous films.
Another issue I had was the big final twist. To say it was obvious is a huge understatement; I saw it coming about 20 minutes before the end of the film, and being so obvious, it was hard to get even slightly thrilled by it. It was just so blatantly telegraphed from the moment it was set up.
It's a shame most of the things I disliked were towards the back end of the movie, because it was a let down after the great opening acts and kinda soured the whole experience with a disappointing conclusion. As I said, the final act aboard the Covenant in particular was quite weak - it felt way too short and didn't portray the Alien in particularly good light. Still, overall it was an entertaining movie, and a definite step up from Prometheus. I've actually seen it twice now, and I enjoyed it more the second time around.
Oh, and as I was asked - I'd probably rank it fourth, after the first three but ahead of Resurrection and Prometheus 🙂 Might be a better-made film than Alien 3, but I have a soft spot for that.