I never expected a prequel to Alien, and went seeing it as a summer blockbuster.
So for a 'stand-alone' Sci-Fi movie:
The special effects were superb, amazing, like wooow.
Acting was great (Fassy!).
Movie itself starting out good (intro was amazing, loved the way the Engineer looked), but along the way made me loose interest.
Some very 'Hollywoodish' stuff in here (dialogue, actions, etc. not gonna go in detail here).