Abe's Oddysee is one of the games I would spend hours and hours and hours playing on, on both the PS1 and PC, along with Abe's Exoddus.
The two 2D Oddworld games are the only games that, in my opinion, PERFECTLY combine so many gaming genres. It's a platformer technically, but incorporates many different gameplay elements very effectively into your playthrough.
The game has fantastic graphics and music, with even better gameplay, with some great reasons to play it over and over again. I'll definitely be buying this.