Wii Play Motion is actually a collection of games from various game developers. Its my understanding that Nintendo asked several developers to come up with developed concepts that they then took and refined to their own liking and are making a collection of games based on. I say the potential is there for it to be good. But it will be most likely a tech demo at full price like other Wii titles in similar scope.
If your into this type of game I would keep it on your radar, but until the game releases I couldn't say more.