I'm only half way through and I must admit I'm really liking it so far. I had to force myself to stop because it was getting late.
It's interesting watching the story unfold backwards too. Some things seem pretty uninteresting when you first come across it - usually the subtle things that have little meaning at the time - then suddenly you realise its purpose.
Like Zylos said, it's very satisfying. Even if the initial concept starts off a little gloomy - no matter what happens it involves an inevitable death. Nevertheless, it's a rewarding experience that is on a completely different level to a lot of games out there. I also find Dr Neil to be pretty humorous, and I'm glad there is an element of humour in the game. Comic relief is needed in an emotion-inducing story.
The only negative things I have to say about it is that there seems to be a fair bit of lag that detracts from the overall experience, and that every time you go up some stairs having clicked a location to head to, the move route is interrupted and I have to click again.
Oh, and there's this one time where I had a sideways hourglass icon over the stairs instead of feet. I can't remember which area that was in, though.
This is definitely one game I'm glad I got. Very nice work.