Pathfinder nicely fits into the classic fantasy setting most people think of when they think of roleplay or DnD. It was created by a group of devoted gamers who weren't happy with the route DnD took with its 4th edition version and was built on the DnD 3.5E open game licence.
"The Pathfinder Roleplaying Game puts you in the role of a brave adventurer fighting to survive in a world beset by magic and evil!
Take on the role of a canny fighter hacking through enemies with an enchanted sword, a powerful sorceress blessed with magic by the hint of demon blood in her veins, a wise cleric of gods benevolent or malign, a witty rogue ready to defuse even the deadliest of traps, or any of countless other heroes. The only limit is your imagination!
The Pathfinder Roleplaying Game is an evolution of the 3.5 rules set of the world's oldest fantasy roleplaying game, designed using the feedback of tens of thousands of gamers." - Paizo