It's indeed a Year Zero Engine game -- same as Mutant Year Zero, Coriolis, Tales from the Loop, Things from the Floor, Forbidden Lands, Vaesen, and the upcoming Twilight 2000. Free League makes not insignificant changes across most of these games to fit the genre, and I really like the pushing mechanic they use in Alien -- the stress that mcneils5 mentions. Cinematic mode is really, really cool, though I admit for longer term play I'd probably look elsewhere... such as at Coriolis. I've heard though, that some people really dig the meat of the background in the book -- a lot of which comes from the various Dark Horse comics, from what I understand.
It's a gorgeous book, too... as all FL products are these days...