Mario Galaxy. You collect stars, but it's set in space this time. You travel from planet to planet (small planets mind you - you can run around them in a few seconds really) and you blast from one to the next. Each one has differing gravity, a variety of enemies, and cool puzzles.
There was a section about it somewhere here on WiiChat, but I think it was removed when the forums / sub-forums were rearranged.
And I have to disagree about Mario Sunshine. I thought it was really cool. The water sprayer worked well, and was loads of fun. The mechanics were the same as Mario 64, and while the story wasn't that great, it was still good to play through at least once. It didn't have the same replay value as Mario 64, but that's probably because it had a fairly steep learning curve, unlike Mario 64. I think the water cannon just wasn't easy enough for some people.