I think Boom Blox is an excellent game. Got to be the best non 1st party game for the wii. The game mechanic reminds me slightly of wii sports bowling. But you target the ball with a reticule and instead of pins your knocking down castles, exploding blocks, see-saw's and all manner of whacky things.
There are also some game play elements similar to Jenga teasing out blocks from rickety structures, the whole wiimote interface is brilliantly realised and makes what is a simple gameplay mechanic very immersive. Some levels have a puzzle element others use water hoses or laser guns to destroy and move blocks.
I love it and so do my 2 boys aged 6 and 11, this is an essential purchase for wii owners.