Very fun 3D platformer, plenty of secrets without being an overwhelming collectathon, not especially hard (honestly it would be nicer if the combat was harder), and doesn't overstay its welcome. You can 100% it in a day if you've played it before.
The N64 version has the same content as the PC version, but worse music (still good though) and graphics. Since the PC version doesn't play nice with modern controllers though, this controls much better. The Dreamcast version is slightly modified from the PC version, the PS1 version is a downgrade, and the PS2 one overhauls the game in a hit-or-miss way.