For games I've personally played:

New Super Mario Bros. Wii
Super Smash Bros. Brawl (you might get into it more once you start unlocking characters and other content, not to mention the large variety of game modes)
Mario Kart Wii
Donkey Kong Country Returns
Kirby's Return to Dream Land
Kirby's Epic Yarn (it might be a bit too easy for your tastes, but the unique yarn style gameplay and graphics might interest you)
Rayman Origins (if you don't already have it for other consoles)

Keep in mind I'm a big 2D platforming fan (it's my most favourite game genre), so my list might be a little biased. Okay, it's insanely biased. But all of those games I listed above have generally gotten scores above 80% and have been selling a large amount. Also, if you don't have anyone to play these games with, they probably won't be as enjoyable.

As for games I haven't personally played:

Super Mario Galaxy/Super Mario Galaxy 2 (many sites regard these two as the best Wii games ever)
Legend of Zelda: Twilight Princess
Legend of Zelda: Skyward Sword
Xenoblade Chronicles (it's insanely good from what I've heard)
The Last Story
Pandora's Tower (if you live in Europe, it's not released in North America)
Sin & Punishment: Star Successor (it's extremely difficult though)
Monster Hunter Tri