Before Wii: What essential GC titles I'm missing?

[taurusnipple]

Shoot yourself for owning this : Mortal Kombat: Deadly Alliance

However, try getting hold of that Treasure developed Wario game, Wario World.

[yosai]

I would also recommend Hudson collection vol 2 : Star Soldier if you like your shooters.

[Champloo]

Ok, not essential but FF: Crystal Chronicles is a good title. Might be worth adding to you collection.

And there's also Harvest Moon: Magical Melody as well as A Wonderful Life. Probably worth owning both if your a HM fan.

Edit: Just noticed, you havn't got Luigi's Mansion!