Dungeons and Dragons. There is no end really, the only limit is your own imagination.

Is chess vs computer less enjoyable as, or more fun than against a person? For my game Skyrim is the one if I had to choose, mainly for the cool exploration.

I wanted to pick this too, but I figured the OP meant video games. Oh well. If it's any game - and with any number of other players available - then DnD wins hands down.

Age of Empires II

M&B warband

Probably Fallout 3 with mods... My mods that is.. Since I would be playing it forever I would have plenty of time to fulfill all my Enclave fantasies there.

It would probably be WoW. Its large enough and is added onto frequently enough to have new content on a regular basis. I had a friend try it out when the Cataclysm expansion was released and he quit after a month citing that the game was so huge there was no way he would have time to devote to it.

You can also use New Vegas mods.

But no Enclave there. I am referring to my two Enclave projects, both of which currently in somewhat playable stage and though the released versions are buggy an observant user discovered the problem was not with the mod but Nexus which had managed to corrupt them.

Two massive projects... And I wasted months trying to fix problems that did not even exist....

That svcks. And I realize you meant your own mods, just felt like shooting in that little note.

Have you taken them down, or are they still up?

Oblivion

Still up and I'm scratching my head on how to work on them again. I got important exams next month so they are on hiatus for now. Can't focus.

Any game? No doubt a homebrew take on pen-n-paper D&D 3.5 or Pathfinder. I never get tired of playing tabletop RPGs, it's just so hard to find a good group for the long term.

If you are talking strictly about video games, then it would probably be Medieval II: Stainless Steel. As much as I love RPGs, strategy games offer the least repetitive gameplay and the most replayability.