Heaven. Actually I think I may go out and call it: this is the best game ever made. This beats Bioshock, which for me is saying a hell of a lot.
It's pure perfection. All flaws are incredibly minor, if they even exist. In terms of comparisons...I'm at a loss. I guess if you've read/seen The Road you have a pretty good idea of the general feel, though that work is a bit darker for sure. Do yourself a favor and buy it, you won't regret it.
Also, I clocked in at 16 hours 30 minutes on hard. I missed a comic and a shiv door or two, but I felt I was pretty heavily dedicated to looking around.
This thing is amazing