HALLOWEEN 4: THE RETURN OF MICHAEL MYERS
After the third (what I think is the best of the sequels) Halloween performed poorly, the studios did the only thing they thought logical- give them Michael Myers. Key word: thought. With Carpenter having now left the series as executive producer and only being involved by having a check delivered to him anytime his theme is used, the creative control behind the sequels took a nosedive.
Granted, this is the Halloween sequel that is a part of Halloween nostalgia. It's the one they would always show on cable around this time. Put next to Halloween 5, it's actually a decent movie. Put next to Halloween: Resurrection, it's fucking work of art.
The lesson we can glean from this movie and its successors it is this- the continuation of the Myers character and the mythology that surrounds him is no longer spooky.