Phantasm IV: Oblivion -- released ten years ago. Supposedly the storyline was written such that outtakes from the original 1978 film could be used. It's also by far the lowest budget film of any of the sequels and shows it.
I like the original film a lot, and found the first two sequels watchable. This one is just confusing, not creepy, and would be totally incomprehensible if you're not familiar with the other three movies. It plays up the "all easy chicks are evil" theme while downplaying the "compressed reanimated corpses make good slaves" bit, finishing with a very ambiguous ending that cries out for another sequel.
It's with mixed feelings that I await Phantasm V, supposedly to be released this year.