Well it would depend on the RPG you are looking for. If you like Online RPGs, known as MMORPGs, Massive Multiplayer Online Role Playing Game I highly suggest the following:
1. World of Warcraft (4 Years Experience)
2. Everquest 2 (3 Years Experience)
3. Star Wars Galaxies (2 Years Experience)
4. Guild Wars
offline RPGs, otherwise single-player, I HIGHLY recommend the first, as it is un-arguably the best game I have ever played
1. The Elder Scrolls IV: Oblivion (If god shat onto a disc, then this is that game, nuff said)
2. Star Wars: Knights of the Old Republic (Damn good game, made by the same company that made Dragon Age Origins)
3. Mass Effect 2 (VERY GOOD GAME, I highly suggest playing, however, playing the first is highly recommended, because the choices you made in the first, affect you in this one)
4. Mass Effect
5. Star Wars: Knights of the Old Republic 2 (Very psychologically dark game, not as good as the first, but still a notable game.)