in one word, Fantastic.

The demo is a short one, lets you have a little play with the basic game mechanics (fighting, basic stealth play and the detective sections) the story has twigged my intrest majory still nothing given away but enough to make me want to buy it on the release, i would say play the demo, although it doesn't show the XP system in use just gathering xp, which are bats that surround the victim and joins your xp pool in the top left.