Come to think of it, has anyone ever seen a sci-fi movie where an aggressive alien species invades the Earth, takes it over and either wipes out or enslaves humanity thus giving the movie a dark ending?
The only one I can think of is "Invasion of the Body Snatchers".
Skyline. Well, it ends before any real resolution happens. I can't recall how they end Battle: LA now either...
Oh, in a little nod to that classic SF ep, in Rage there's a book you find lying around called "To Serve Mutant".
The Jedi Master