How about something like Skyrim? Single-player, available on the PC, hundreds of hours of content, and it's not D3 or WoW. Kind of immersive, though.

Alternatively, Minecraft! Single- and multi-player, available on the PC, limitless content, it's not an RPG, and you start again where you left off every time (you can even exit mid-jump and return to finish that jump three months down the line).