The lights are on
Things in life are often better when you have a friend in tow, and gaming is no different. Come find someone to watch your back.
For me it's a toss up between Borderlands and Champions of Norrath. (fond memories)
Either Eragon or Lord of the Rings: Conquest. And I just realized how ridiculous that sounded. Conquest is actually really fun with a few people splitscreen, though I never play it alone.
I think Eragon is a good hack and slash game. Plus it had PC co-op on the same screen and computer, which is incredibly rare. The characters differentiated in their abilities as well, which was a nice touch.
Sa kyr'am Nau tracyn kad, Vode an.