For calibration purposes: I loved the first one, and thought the second one was decent. Hell on Earth was complete garbage (leave the puns to Freddy, please) and Hellraiser In Space was notable only in that it was even worse than Leprichaun In Space, which came out that same year. I haven't seen the others.
I just watched Hellraiser: Hellseeker (which is apparently Hellraiser 6) and -- though I know this will be hard to accept -- it was actually pretty good! It was more of a psychological thriller than a splatter movie, so it really wasn't much like the other Hellraiser movies at all. It was very hallucinatory, and through most of the movie it's hard to tell which events are real or even what order they are happening in. I'm a sucker for that kind of thing. The acting was decent, and the effects are low-key enough that their budget didn't show.