Super Mario Galaxy is a brilliant game. As is Resi 4 and wii sports. They need to get a new HD Wii out that has more accurate controls- then we'd all be rushing to play it again!
The motion sensors are actually incredibly accurate (look for some videos of people tinkering with them on their pc on youtube), the problem is coding anything half decent for them. For example, a light-sabre game, everyone wants one, but little do they consider that how exactly, when they clash their saber against the enemies, will the wii-mote kick back and stop it from just passing straight through, thus breaking the entire game mechanic?
Its input is accurate, but its output isn't... which is unfortunate now i think about it, the image of children being punted across the room by their wii-mote because they got tackled in NFL is a rather hilarious one.
But yeah, one won't work without the other.
I also rarely play games now that don't rewarded me with achievements either. I live for achievements. 
