I really liked the story, there was a healthy amount of suspense and intrigue. I saw a lot of similarities to 'The Secret of Daphne', another story I thoroughly enjoyed.
The characterisation of the protagonist and the teenagers was quite good and felt genuine, maybe certain parts relied slightly too much on the dialogue, but that's a very minor point. I haven't played the game enough times to judge how linear it is, but I noticed there were several different endings, which is a big plus in my book. The choices also seemed reasonable, I thought 'The Dead Man' in particular was a really nice twist.
The main reason I can't rate it higher is because I noticed several typos (admittedly hard to avoid in such a large story) and a couple of times where the grammar wasn't perfect. Fortunately this didn't affect the flow of the story, and I was engaged to the end (except for maybe one overly long page, but that one had a great twist at the end of it, so it was worth the read). In the end I rated this a 6/8, but I think it could become a 7/8 with some polishing of typos and use of dialogue, and a more original beginning.