hm... for graphic quality? Probably Mass Effect. Beautiful graphics and extensive 'go anywhere you want' environments.
For fun gameplay? Assassin's Creed... nothing more fun that slaughtering everything in sight, while staying out of sight.
For story? Soul Reaver / Legacy of Kain series. Those were some of the best games I ever played, and I hate not having my PS2 anymore =(
Best overall would have to be Starwars: Galaxies before the CU, back when it was good. Great community, fairly fun gameplay, huge areas to explore, everything was player-created including entire cities, pvp was decent... Unfortunately Sony smashed that game to bits when they tried to make it 'better'.