A grand piano is better than a kid's Casio keyboard.
Like a musical instrument, the computer keyboard takes practice, but after holding my fingers in the WSAD position for years, I can say my fingers slipping is not really an issue, and the sheer number of keys available to map to a game makes it much, much better than a gamepad to me.
It might not be the best control option for beginners, but the combination of a keyboard for body movement and a mouse for looking and aiming, I have yet to find anything better...unless someone puts an analog stick or rudder on a keyboard, which would allow for adjustable walking, running speed...but that's not very essential.
I am not trying to be a fanboy, I truly believe that a keyboard and mouse are the most versatile, accurate, fast, and customizable control options available. Turning speed with a mouse is never a problem for me, moving up or down relative to the mouse's position has never bothered me, and while a nunchuck is more comfortable to hold than a keyboard, it has all of 2 buttons, a joystick and motion controls...which can only get you so far.
You can play Valve games with a gamepad, or a gamepad+mouse, it's in the control options. Console gamers might prefer it.
But I submit that most that hate keyboard+mouse hate it because they are not used to it. Once you get used it, you'll find that nothing on the market today can beat it.
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )