The big problem with third party Wii games I've seen is they can't seem to figure out how best to use motion control (some exceptions apply). Most often third parties grossly overuse motion control, shoving it into places it has no reason to be in. They seem scared to use the Wiimote+Nunchuck as a tradition controller, only using motion control as an additional button or two.
Nintendo does this very well. Most of their games (Galaxy, Twilight Princess) use motion control, but don't overuse it.










