While Rayman may be known for his 3D adventures, most forget his true origin. He debuted in a 2D platforming game, and it was exclusive (for just a week) on the Atari Jaguar.
The Atari Jaguar version (being on a cartridge) was missing many areas, and featured inferior audio and visual quality compared to the PS1, Saturn, and PC versions. A GBA version came out many years later as well.
But as far as the actual game, it was a 2D side-scrolling platformer like Mario, Sonic, and Earthworm Jim. He must pass through six different worlds to complete his quests. With additional powers gained each step of the way. You would need them as the original Rayman provided a tough challenge from what I hear.
The game was well-recived by critics and gamers alike, though it would increase the series' popularity with the further sequels. Rayman found a lot of fans in United Kingdom as it was the number one PS1 game in the country beating out games like Tomb Raider II and Gran Turismo. I never got the chance to play it myself but I hope to.