As JSH said, the sound is pretty key. I think the graphics are quite unique as well.
That being said, the interaction was a bit limited for me. Understanding that Tilt isn't a "game" per se, I still feel the player could be provided more choice, or at least the illusion of choice.
Perhaps more people and objects could be interactive? While I understand that Void is obviously not a denizen of the real world, so his powers to affect it are limited, maybe certain objects could cue optional sections of story, further explaining things. Or perhaps there could be optional areas in the same vein?
Criticisms aside, it's very original and I like the structure of it. An interesting game in the same vein is called Every Day the Same Dream, although it is somewhat more interactive:
http://armorgames.com/play/6244/every-day-the-same-dream