Reasons why this movie was bad
The most important, to me, is that they spent a considerable amount of time in Prometheus hyping up the mystery of the Engineers, their motives, and what would happen when Shaw met them. Then we never get to witness this meeting.
And, was this the Engineer's home world? Cause it seems odd that an entire planet's population could be wiped out by one spaceship's cargo worth of bioweapon material.
Also, the deaths were fairly dull. The one that annoyed me the most was Rosenthal. When David rescues the crew and takes them to the city they ask him if it's "safe there" and they just take his word for it when he says yes. But you can clearly tell that there are several wide-open entrances into the city and the alien is still wandering around somewhere. But do they care? No, they just go wandering the city alone without a care. And sure enough the alien just waltzes in there easily and kills Rosenthal. How did they not foresee that as a possibility?
And most of the deaths were uninspired. I guess there's only so many ways that what is essentially a feral animal can kill a person, but by this point it just seems like we've seen this all before too many times. There's nothing scary at this point about watching a Xenomorph sneak up on a person and maul them to death. That is one thing I liked about Prometheus. There were all kinds of alien creatures so there was a lot of variety in the ways each character died.
Oh, and at what point did Lope become infected with a "protomorph"? Did David somehow bring a face hugger on board or was Lope infected while still on the planet? They never explain this
Finally, how fucking stupid can they be? Gee, these two robots look EXACTLY THE SAME but there is absolutely no way that the psychopathic one could possibly try to impersonate the good one. Accents are impossible to fake. Lets not even take ten seconds to explore this possibility.
There are probably more examples of what the writers got wrong in this movie but these are the ones that immediately come to mind