My primary problem was the numbers keys. I really can't think of any good way to do this with just the keyboard. You need the keyboard to move and you need it to attack and change between accessories. Three things you have to do with two hands. Ctrl+space or shift+space would be better if you don't want to use mouse. With the mouse, though, there's an intuitive interface. With one finger attacking and the other switching weapons, there's very little hand movement necessary. The more the player is moving his hands, the more trouble he's having with controls.
I used the browser version. Would the Windows version have been a different experience?