Ahhhh, a question about this topic. Everyone knows MY OPINION.
I don't know how long you've been a PC gamer, but if you recall the early FPSs that were keyboard only, a console controler is slightly better than that.

Ok, it's much better, but still complete blah when compared to a keyboard and mouse.
Developers generally put the AI in tard mode and add auto-aim when producing FPSs for console, this way the guy aiming so sluggishly with their thumb can feel good about themselves and not get frustrated. If you're used to the really good PC FPSs, you'll see that most console shooters are on Prozac at a petting zoo.
What really sucks, is that most PC games now days, are ported from consoles. These games are always really bad on the PC and not worth buying.
The only exception to this is the Wii and its controller. It's about as good as a 200 DPI mouse, IF, your sensor bar setup is in a good relation to your TV. There are a few factors which can make it difficult to use like distance and TV size, but coming from a mouse and keyboard, I found it second nature. The Wiimote also has a stick attachment for movement, which can be better than a keyboard when a game doesn't require loads of options.
Anyways...
<]=)