It's easier with a controller... to be honest, I recall buying a controller for it because of how it made my fingers stiff after a while. Also, it is hard to do diagonals without a thumbstick.
Edit: The gameplay is actually fairly enjoyable once you get a wider variety of weapons and finishers. It is also fast-paced. However, you spend a pretty ridiculous amount of time fighting in the game, looking at it in retrospect. For early bosses, I was pretty dependent on the dual sub-machineguns, though. One of the earliest bosses moves way too fast for the close-range moves unless you have high gaming skills or are just obsessed with killing everything with melee attacks.