Phantasm III: Lord of the Dead
I think Phantasm II would sit better in the franchise if Phantasm III had followed up on it in a meaningful way. The biggest addition of II was Liz and her psychic link with Mike and the Tall Man but since she's tossed like gutter trash in Phantasm III and Mike is played completely differently, it makes Phantasm II a little pointless and an anomaly to the series. There are some great shots and parts to Phantasm III but I think it's mostly bogged down by silly zombie characters, new sidekick characters that do not provide anything new to the franchise and will also be quickly discarded and by giving Mike little to do.
Phantasm IV I really enjoyed because it lost the silly humor, did not focus too much on new characters that will never be explored again (instead it even brought back the fortune teller - nice touch), it returned to the low-key surrealism of the original, answered questions but left you with more and brought back the themes that made the original thought provoking and not just a "typical horror picture". I also thought the ending of IV was a genious ending to the series if they close it out that way.