Witcher 2 UI was easily playable with keyboad and mouse, if you have the brain capacity to do it.
No, The Witcher 2's UI works terrible with keyboard and mouse. Inventory and skills screen are overly large and a pain to navigate through. When you're highlighting an item in the inventory list it triples in size, discards weight/value info and adds category info. This drastic change makes the list a pain to go through with the mouse, and it actually works better with the directional keys. The mouse is all about precision, you don't want objects to change in size when you hover over them - you want to do that on a gamepad though, to tell where the hell you are.
(Also, what the hell is up with the World of Goo design on the ability screen? In Skyrim, you fly through space to pick a perk. In The Witcher 2, the ability tree is made up of goo balls that wobble around when you hover over them. I- I don't... Why are UI designers insane?)
Worst is dialogue. The dialogue options keep jumping around over the screen, forcing you to chase it down with a topping of mouse lag. This works on a gamepad without hassle, but with keyboard and mouse it's just another spit in your face from this half-assed console port.
Discredit where discredit is due.
The Witcher has OK UI though. The talents screen could've squeezed everything into one tab instead of 4, other than that, it's OK.