I would suggest the already mentioned Borderlands Series and Elder Scrolls series, and also suggest Fallout 3, Fallout New Vegas and Fallout 4. New Vegas is more RPG than the other two but they are all exploration FPSes.
Do you have a windows PC? How old is it?
Some of the recommended games are 10-15 years old and are not as graphically demanding as they were when they were released.
