In terms of best graphics, Crysis. If you want to do something with your computing muscle other than pure eye candy, then I recommend Mount and Blade. It's an rpg typa game where you command the general of an army, in battles you control your own character and give orders to the soldiers - very fun
The main game limits you to about 150 people on screen at once, but you can get a mod that expands this limit to 10 000. Medieval warfare including awesome seiges and cavalry charges with 5000 soldiers a side!







