Eh, it really differs from game to game. Some games that should work fine with keyboard and mouse have menus and functions all made for a controller and get a really poor port. I've seen some gameplay of Splinter Cell: Double Agent that looked pretty clunky, and that's a third person shooter. Plus, with how many games are designed for console first now, the controls have a lot of contextual stuff that really doesn't translate to a keyboard so well. Look at Assassins Creed for example. That series is swimming in context, what's handled with a radial menu or a pressure sensitive trigger ends up being several buttons.
