It would probably do you well for Wiiware, but well thought out and implemented controls are an ABSOLUTE MUST. My suggestion would be to use MP3 as a base and add in a quick turn function based on flicking the Wii remote while pointing outside of the screen range. The - and + buttons could work for switching weapons, and you could use pointing the Wiimote straight up to activate reloading. B = shoot, A, Z, and C can be put towards Jumping, Ducking and Maybe activating a powerup or using a secondary attack or feature of your weapon (attack with the butt of your gun if out of ammo, or activate the scope on snipe rifles)
you could also have it set so that shaking the nunchuk while moving caused you to throw yourself in that direction so you can attempt to dodge out of the way of incoming fire.
One thing I rarely see developers do that I would see as a huge selling point is the ability to adjust the sensitivity of the waggle on the Wiimote and Nunchuk, that way for the people who find it activating too easily, they can turn it down, and others may feel it's not activating easily enough can turn it up.
Of course, 1 and 2 buttons would be to access stats and other options, such as adjusting the waggle sensitivity. Oh, and I forgot about the Dpad, maybe use it to navigate the option menus that you pull up using hte 1 and 2 buttons? that would let you adjust those things and still be able to move around and shoot at stuff. Otherwise it could be used for quick weapon slots so that you didn't have to cycle through allthe weapons to get the one you wanted.
(heck, if I could get an online competitive FPS for the Wii that actually made good use of the Wiimote and Nunchuck, I'd be willing to pay a lot more than just $10 for it)
If it's a $10 game for the PC, I could easily see that going for people with lower grade PCs, who may not have a PC build capable of handling the big FPS already out there like TF2. So the issue here is making sure you keep it so the graphics options can be turned WAY down.
I just really don't see it being feasible for 360 unless it's a really quirky game with a style completely different from Halo and CoD, GoW, and TF2, 360 is just incredibly saturated with FPS that there's just no way a $10 game can compete with those if its not incredibly different.
PS3 I'm not sure about. It's not as saturated as the 360, but it still has stuff like TF2 and CoD, and possibly a couple others. Again, a key issue would be setting yourself apart from other games in the genre