I watched FD4 a few days ago. Better than FD3, ending quite similar. But the first one is really good, second is ok. Third one is the worst, FD4 bounce back a bit.
Anyway, I think FD4 put too much bloody scene, makes the audiance forget the clue about died one by one~ Only the first one make your thinking about it after watch it. other three aren't that tempting.