Sales do not indicate quality. Toyota sells more than Ferrari. If you like the Wii, that's fine though.
I find CoD4 to be a great FPS. It does many things right. Obviously, graphics are great, multiplayer is fast and has a lot of features. It has ironsights as well.
Yes, I've played the Wii before and I almost got one. By original games, I mean hits that aren't derived from the gamecube. Resident Evil 4, Twilight Princess, Mario Galaxy, Brawl, Metroid 3 have all had previous versions on the gamecube.
CoD4 is great on the xbox 360. It supports the right amount of players, it has voice support, it adjusts team imbalance and you can add friends easily. I'm very comfortable with using dual-sticks for FPS.
All the consoles do different things. The Wii is great for introducing non-gamers with light games. The PS3 has blu-ray and a free online network. The 360 has many deep games and an online network with the most features.