Oh it's monstrously popular for a reason. Though...on the underground side for some strage reason. Not that I'm complaining. The original game is already about $120/copy.
I'd say get the second one while you can, since the developer, for some reason, only makes limited copies. I haven't finished either game, but from what I can tell, the 2nd one is pretty much the 1st one with a different story and better graphics.