I had Spyro on PS1 many years ago, and I've actually found Eternal Night much more playable. Am only about 3 hours in so far, but the game takes you through the various controls in a very simple way as you begin to play, so they're not hard to pick up.
As the other reviewers have said, it is much darker than the PS1 Spyro game (well, so far at least), and is also different in terms of the game play. Eternal Night doesn't have the annoying repetitiveness of the PS1 game where you were constantly hunting for that last jewel; instead it builds on the problem solving and bashing enemies parts, and jewels are needed for other things like energy and special abilities.
All in all a great evolution of a fun game.