If you would prefer a game that gives you a lot of freedom to roam around a wide open world in a non-linear manner with a ton of side quests that you can choose to complete, go with a Bethesda game like Elder Scrolls Oblivion/Skyrim (swords and magic) or Fallout 3/New Vegas (guns and medicine).
If you would prefer a more linear game that puts a lot of focus on dialogue choices and relationships with NPCs, but still has a ton of side quests, go with a BioWare game like Dragon Age: Origins (swords and magic with tactical battles) or Mass Effect (guns and psychic abilities). The Star Wars: KOTOR games are also fun but they might seem outdated by today's standards and they don't include adult content (meaning sex) like the other BioWare games do.
If you prefer more traditional RPGs that focus on stylish Japanime and musical score as much as (if not more than) the actual gameplay and story, go with a game like Star Ocean or Tales of Graces.
Finally, if you like to try RPGs that are unique, have massive boss battles, and that could be challenging enough to make you want to throw your controller through the TV screen, try Dark Souls or Dragon's Dogma.