I HATED the repeat playthrough games. It's such a damned letdown. I guess they wouldn't make a game like this that ends with just a giant fly boss though anyway.
I remember playing this on an emulator in college. I lost count of save state restores somewhere around a couple hundred and just went into an awe-filled trance where I wondered how anyone could possibly beat this thing.
It didn't help that the layer effects were fucked up on a lot of levels. The fog (lava?) one where you float around on a platform was crazy with that.