Is this piece of plastic worth it?
The Wii Zapper concept has been around since E3 2006, where a prototype was shown in a display case. This first example differed drastically than the version that is being made available to the public. It did not involve the Nunchuk in any way, instead including its own control stick and trigger button. For good or bad, Nintendo obviously realized that all Wii owners already owned all of the necessary buttons and control devices, so they opted to instead release a simple piece of plastic that both a Wii Remote and Nunchuk could be firmly connected to.
The only button on the device is the trigger. This is simply a hinged piece of plastic that relies entirely on pressing the B button in the Wii Remote. It's obvious that the designers intended this to be the primary means of interacting with games designed for the Zapper. In fact, the way the unit is put together renders every other button on the Wii Remote all but useless, as they can't be reached in any comfortable or quick motion. Thankfully, the Nunchuk is mounted in such a way that both the Z and C buttons are accessible, along with the control stick. Do the math, though. That's only three buttons, so don't expect many complex gaming experiences to come out of this device.
Probably the biggest knock against the device is that it actually makes games harder to play. In Link's Crossbow Training (the game that comes with the device), I would routinely score higher when I held the Wii Remote in my hand. This is due largely to the fact that I had much more precision in simple wrist motions than I did trying to move the entire Zapper assembly. There just isn't a perfect way to hold it. Everyone who has picked it up and tried to play with it has gone through several different methods of holding it before settling on one and commenting that nothing felt quite right. Overall, it's just quite awkward. The instruction manual even suggests taking the Nunchuk off and holding it in your left hand while holding the Zapper in your right. This feels cool, but fails in practice. You will immediately start holding the Zapper up to your eye to aim (much like aiming was done with the original NES Zapper). The pointing device of the Wii Remote doesn't work in this manner, as it can't account for different television sizes, so the precise aiming does not help at all.
If you had to place the Zapper somewhere on the spectrum of Wii accessories, it would fall much closer to those silly Wii Sports attachments than the Nunchuk or Classic Controller. If you think you'll have more fun shooting something that feels more gun-like, feel free to pick it up. If you think you need it to play any of the shooter games coming out, think again.