Mmmm those movies you mentioned are even better and I haven't seen much from TROMA only: Graduation Day, Angel Negro and Toxic Crusaders.
The sequel is boring most of it is just flashbacks of the 1st film.
I'm getting part 2, part 4, and part 5 for free though. Part 3 was a bust, I hope there isn't any continuity between 3 and 4. So, surely I won't be too disappointed. I liked Prom Night 3 and 4 afterall.