Graphics don't realy matter much to me when it comes to replay value, but oblivion was one of the games i felt that when i did upgrade my pc, it deserved to have another shot with me, because it was quite a bit of a let down when i first played it only to find i had to have the graphics far worse then morrowind to get a playable framerate. When i did get my new rig though, i did install oblivion to try it again and it was much more enjoyable with max settings.
I don't think i had any other games that would have made much difference in gameplay/fun when running them on max settings instead of low settings.