Don't care if it's game or not,
for me it's a piece of interactive literature, first of its kind. It's better than a movie, it's better than a game (in achieving it's goals, not per se) - it doesn't force anything, just lets you explore the story, at your own pace, gives you time to have a thought, listen to the sounds and music, or look at the environment - just like a book, but with broader spectrum of senses being involved. It's best 1.5h I've spent in a long time, I got really into the story, both intellectually and emotionally, and got a genuine katharsis at the end; God, I barely remember that feeling! And it's interesting to see this new genre being, hopefully, born. Games that are not only entertaining, but also aim at artistic and cultural goals.
So the bottom line is, buy it if you want an interesting, immersive experience. It's not something you will like, if you want specificaly a game. in traditional sense. This one goes beyond. Than get a coffee and a piece of cake, dimm your lights, put on your headphones, get into your bed with your laptop, and open the first page.