If they had pushed the Xenomorph at the side to focus on Engineers and provoke some serious ideas and questions (as in Blade Runner) I would get totally hooked, and I would embrace the whole trilogy of those movies as a welcoming addition that deepens the whole Alien franchise (certainly more welcoming than Alien Resurrection where we have Xenomorphs and Chestbusters and everything, but that doesn't add anything valuable to the Alien universe.
However, Prometheus didn't really touch me.
In Prometheus Human kind is obviously a spacefairing race that is teraforming other planets, and they have obviously never met another intelligent race.
The discovery of another intelligent race is something that would leave everyone in shock and with questions that would left them unable to sleep next night.
Everyone, the biologist, the religious, but also the garbageman, the policeman... everyone. Well... except maybe David.
The reaction of Prometheus crew?
Elizabeth and Charlie are the only ones excited about the discovery. Everybody else behaves like nothing special had happened.
And then they discover that we share DNA with engineers... that engineers are possibly our creators.
Again... Elizabeth, Charlie and that female doctor seem excited.
The rest of the crew is too cool to be excited about discovery of another intelligent race, and possibly our creators.
And naturally I didn't feel one bit excited either.
And the movie was supposed to let us with this big question "why the engineers want to destroy the human race".
Shawn was the one that concluded that engineers used black goo as a weapon, and she concluded that engineers wanted to destroy the Earth, however... those are all wild speculations on her part.
It's not like she find a engineer memo or something that says "have breakfast, destroy earth, grab a shower"... the writer blames the audience of Lost for not tying the loose ends, however if audience has to tie too many loose ends then the writer leaves too many loose ends.
And finally, if one wants to make an epic trilogy than one writes the script for the whole trilogy before starting to film the first movie.
Going like this... three different movies, three different scripts, and probably three different writers will most probably end up as giant mess.