Feel free to skim/skip sections.
I have played First-Person Shooters since I downloaded the Demo of Castle Wolfenstein on a Bulliten Board System over phone lines before the Internet was "unleashed" around 1992-1993. I was the first among my friends to properly separate my keys in DOOM so I could strafe and circle them at the same time, killing them.
Quake took me by surprise, and it was a year before I figured out the mouse. But I've never looked back.
Why FPS with your Thumbs is Dumb
I bought a "SmartJoy FRAG" (which allowed for emulated Mouse and Keyboard controls on the XBOX) from Lik-Sang (which Sony killed) and got on Halo 2 with my cousin, who was once in the top 50 U.S. Players. He showed me where the guns were and in two games, my percentage score went from 3-4% to 93%. The other guys on LIVE thought we were lying and I had handed off my "controller" (well, I had, for the SmartJoy FRAG) to another person.
It proved for me, once and for all, that trying to aim a crosshair with your thumbs was stupid. Thumbs are not naturally dexterous appendiges - they grab things. When you use your thumbs in PS2 and XBOX FPS games, you are essentially trying to align two crosshairs - one involving movement, the other aim, at a moving target. I tip my hat at folks who, like my cousin, can do this.
All the while, I've had to get my FPS gaming on my PC. Half-Life 2 and its MODs "Day of Defeat", "Counter-Strike" and lesser knowns have been my main-stay.
I own an XBOX and have never bought an FPS for it other than Halo 2, which I ultimately gave to my cousin when he broke his (stepped on it, dumb-ass). I ended up buying a PS2 because so many games for the XBOX were all FPS... with your thumbs!
Enter, the Wii
It could have problems - it's all about the bounding area, but I've read that Metroid has it solved. I must admit I'm actually enticed - far beyong the PS3's promise of allowing a USB keyboard and mouse for playing Unreal Tournament 2007. In that case, Sony said "Developers have the option of supporting a mouse and keyboard." Glee. That means, many won't.
We all know that whatever COMES with a console BECOMES the standard. No add-on has ever succeeded to become saturated in the existing market. That's why the N64 had four controller ports (I never owned one because I thought cartridges were stupid compared to CDs, until my cousin sold me his).
So anyway... that's my take.
It is the first time since the mouse entered the picture that a good control scheme has been cooked up - because I have never seen a gun game that allowed for completely free movement as we are used to in our FPS game (correct me if I'm wrong).
This can't be a bad thing, and the Wii should change what controllers we see in the future.