Impressive technological effort!
Good job on the technological side, working with HTML5 must have not been easy!
Please consider, for the sake of the demo, to improve the fonts of the text, because it is sometimes hard to read, but again good job!
Probably a scale factor for the voxel size could help the graphic aspect, it might cause an increase count of voxels to render though: I would suggest to search a compromise or add some Math to find a more refined way to calculate the final size of the voxel to be rendered on screen. Probably by including the size of the object to be represented along with its distance from the point of view. It seems that small objects (from what I can understand) occupy the same screen space of big objects (I could be wrong, please kindly verify what I am saying).
Good job again! It is an impressive demo!