GTA runs pretty poorly at my computer, but still is quite fun. (how many loose ends do you have to tie up in the end of the game? It's like - ok, here's teh final mission.... no wait, here's another one.... wait, let's haev another final mission)
On the other hand, GTA has pretty much strictly told me, to get a new PC before I can't run ANY games at all... Fallout only asked me to go to the medium settings, while all the other fresh games I play ran nicely