I know on the Wii the Zapper games can really accentuate the flaws in how the sensor bar works. It is just a matter of luck on how the room is set up, and if your unlucky it's like voodoo magic with trial and error trying to figure it out. External lights, like a computer or cable box, as well as reflective surfaces (because of light) can throw off the signal and make your cross hair bounce. There is also the matter of how big your TV is and how far away you are standing, if your not the right distance the cross hair would move to fast or too slow.
That being said, if you can get it to work properly Link's Crossbow Training is awesome. It was originally bundled with a Zapper for $20-$25, but you may need to look around now to get a good price. But it is a fun shooting practice style game with 27 levels, a third are shooting targets and the rest are different scenarios shooting bad guys from the Zelda universe.