Spooky, I just watched the new Blu Ray of Planet of the Vampires the other night. (A huge step up from the early 2000's DVD.) Surely you can appreciate all the in camera effects, (Mario Bava was a master at this) and how much of Alien is lifted from it. ;)

The derelict alien ship and it's dead crew seriously creeped me out as a kid.

I do agree about the ending, (although the film drops subtle hints early on these people aren't from here) and it's impossible to figure out how or when two characters got taken over at the end.