Metroid isn't a shooter, it is a first person adventure game that has a gun attached to your hand
, so pick up the Metroid Trilogy, as that is all 3 games for $50 this fall.
Anyways, you obviously have your staple games like Mario Galaxy, Legend of Zelda: Twilight Princess, and Mario Kart Wii, but you also have some great titles like:
1) Mario Strikers Charged - awesome arcade soccer. Tons of fun especially with friends in co-op.
2) Punch-Out!! - Twitched based fighter. Excellent game overall both graphically and gameplay.
3) Shaun White (Road Trip came out last year, but there is a new one this November) - If you have a balance board you might as well buy one of these. I have Road Trip and it is a lot of fun on the balance board. If you don't have a BB it isn't worth it though. local co-op is fun to to switch on and off the BB.
4) Fire Emblem: Radiant Dawn - Best SRPG you'll find. If you've never played Fire Emblem (or strategy games really) you would be better off with Fire Emblem: Path of Radiance which is for the GC.
5) Tiger Woods PGA Tour 10 - if you like golf games at all, this is a must buy
6) Godfather: Blackhand Edition - Even if the graphics are lacking, this is the definitive version of the game. I typically don't like sandbox games, but you get pure joy out of beating the crap out of people with your hands or using the Remote/Nunchuck as a garrote
There are a lot of other really good games, but those are the ones that come to mind.