Let's see... since it's forever, I'd probably want to focus more on entertainment and replay value, with overall quality as a second priority.
So,
Minecraft, obviously. Especially if the "ultimate" version specified in the OP included my choice of mods.
To vary it up a little, I'd take
The Legend of Zelda: Majora's Mask (for the "sandbox" and Easter eggs... also, y'know, my favorite game ever, &c.).
And while
Final Fantasy X-2 isn't the best in the FF series by any measure, it is the "biggest" in terms of nonlinearity, mini-games, Easter eggs, side quests, &c.
To round it out, I'd take
Super Smash Bros. Brawl, for the awesome gameplay, gazillion modes, trophy-hunting, &c.
Those four would probably do it, actually. But for variety, I'd take a puzzle game of some kind... perhaps
Pokémon Puzzle League, I always felt that was underrated.
Also: Really, CAPTCHA? Really?