As i said. Fallout 3 has FPS elements but remain at its core a an RPG game. Borderlands on the other hand, though having elements of both is a genre on its own, it strips down RPGs to its bones and use only what it needs to remain fun and discards what would normally make it fall into the niche RPG market. Things such as long boring and complicated Character sheets, Specs, Deep Plots and the like. It does the same from FPS's and brings the two together to form something new. Diablo did this back in the day. Combining the fast pace of a hack and slash with the depth and loot collection mechanic from and RPG.