We had a lot of fun with LEGO Indiana Jones. He knocked the heads off anyone that came to his office! You could make your own characters too, then play them on any of the completed adventures.
Boom Blox is the satisfying combination of Baseball pitching and on-screen Jenga. A must for parties, especially if you get to go third!
Twilight Princess and Metroid Prime 3 were both excellent games that could easily swallow 3 hours' gaming without you noticing.
Super Smash Bros Brawl is the Wii version of Melee but features new moves, online play, new characters and a 10-hour adventure mode featuring some good cutscenes (which could have used some narrative to help explain what was happening!)
Mercury Meltdown Revolution was taxing, moving mercury by tilting the surface it was rolling on.
Mario Kart Wii is a much trickier version of the Gamecube's Double Dash, but the online play is aggressive and the competitions varied and challenging.
No-one's mentioned WiiWare, the new (not retro) downloadable games that vary in quality from low-tec Tetris to hi-tec Helix. They differ in cost.