Could be one of a few::

Oblivion: great game but laggy (Thanks Bethesda)

Fallout 3: again great yet laggy (Thanks again Bethesda!!)

GTA 4: amazing to run round blowing off steam but novelty wears off....

Just Cause 2: Good game until you have found and collected everything... then cd becomes a mug holder..... :D

My choice from the above would be Oblivion as Fallout is a bit too short..... Hopefully the new title ES: Skyrim will introduce multiplayer, they have anew game engine so hopefully the glitchy and laggy graphics will be lessened or even better gone XD