Originally posted by: GodlessAstronomer
Oblivion is pretty damn huge. Honestly if you've seen all of the content in Oblivion including the DLC addons then you should consider playing games less.
That, seconded.
I still haven't completed Morrowind to this day, it was so big and I was so engulfed in modifications that eventually one expansion pack came out, and then I played it, and then just as I actually started the main Morrowind quest then a second expansion was released. Then I played all three, doing countless side quests and trying more than hundreds of different mods over a period of around two years or more, then without exaggeration by the time I was really interested in actually doing the main quest the game's graphics and overall quality was just sub-par for the new standards and Oblivion was only a few months away from release, and I simply lost interest in Morrowind altogether.
The same thing happened with Oblivion, but maybe two times faster simply because Oblivion is so huge that it actually gets intimidating, although the content in it is quite repetitive there are still mods out there almost as big as a real expansion pack, if not actually bigger. I haven't even bought Shivering Isles (Oblivion's expansion). It's just a freakin' big game, there's frankly just too many things to do especially if modifications are used, then it gets too much literally, at least for me it was. Now I'm simply immersed in and enjoying Fallout 3, and I can certainly see myself completing its main quest eventually, because its game world is big enough to give a sense of not being blocked in a narrow world and always passing by the same locations, and at the same time its size is about... by estimation... let's say maybe 30% or 40% the size of Oblivion's map, but the number of side quests in Fallout 3 may be a little small, there's certainly quite less of them than there are in Morrowind or Oblivion.
But, yeah... to answer you directly the only "endless" (virtually) game you can play are those without any obligations for the player, "free roaming" or "free actions" games (Sims, Civilizations, a number of RTS games, and a few others, but they are rare). The best example to this day in my opinion is quite simply said Oblivion, at least in a 3D environment. They are very good games, perhaps too addictive at times, but eventually many players just step away from them because they're just too big and other games eventually gets their attention.