If only specific games and not "GTA complete" -type o packs, maybe:

*Dwarf fortress
*Galactic Civilizations II: Ultimate edition
*KGS or other Go client with whole lot of pro games .sgf's. Would finally have time to go through all Shusaku's games \o/

Star Wars Battlefront 2+removed mod limitations (every single good mod pre-installed)
GTA San Andreas
(Insert DnD RPG here)

Eek; that's hard:

Binding of Isaac - I've already finished everything there is to finish, but there's also a bunch of user generated challenges people have come up with.
Clubhouse Games - This will be my go to handheld game.
Bookworm Adventures Volume 2 - I find that this is a great game to play while listening to other stuff in the background.

Edit: Oh shit, PC games only :( ok, I'll emulate Clubhouse games...shhh, don't tell anyone...

Edit 2: Alright, fine I'll go with Bejeweled 3 instead of Clubhouse Games...

Three games only is hard. I'd probably go with something like:
GTA: San Andreas
Civilization 2
Minecraft

Sacred Gold
Terraria
HOMM 3

Reason: Addictive and amount of content.

Is Battelfront worth it just for the SP?

Sorry to momentarly hijack the thread. :)