The demo itself arrived for Xbox LIVE Gold members last week, but has now been made available for anybody, regardless of whether they're on a PS3 or an Xbox 360. Plus, if you're a PC fan, there's a version for you available now too, via Steam.
This is the first time the franchise has appeared on PC, so it's understandable that there were a few bugs. 2K has reassured us that - less than 12 hours after the demo going live - it's already been patched to fix up some of the more serious issues, and they're keeping an ear out for any further concerns.
The Darkness II is due out on February 10th, for all three major platforms.