The Wii Zapper is a casing unit which holds the Remote and Nunchuck in position so it feels more like you're using a lightgun, it's a sturdy design which feels comfortable and also tidy's the wiring out of the way, all in all a very good design, now this also comes bundled with a game.
Links Crossbow Training is a lightgun style game with various different modes from standard shooting practice, where you aim and shoot at different targets on a static screen, to Ranger where you control Links movement and fight off hordes of coming enemies, all the modes are rendered using the superb Twilight Princess engine and world.
If you like Lightgun games such as Virtua Cop, House of the Dead or Point Blank this is a must buy, at the end of the day Links Crossbow Training is worth £20 alone.
The Zapper is already compatible with several games with more to come.
Ghost Squad - Works brilliantly.
Resident Evil: Umbrella Chronicles - Works OK.
Medal of Honor: Heroes 2 - Works brilliantly.
House of the Dead 2 & 3: The Return - Reports say it works brilliantly.