Brilliant.
Very lego, but also reminded me of Douglas Coupland's "Microserfs" [book].
I would love to see the grid square differentiate when you are above it, to be sure of accurate block placement. Something like the border getting darker, or the square getting lighter.
I'd like to see better connections between the pipes, and the fence-like tiles that go on the outside of the squares.
Perhaps you could make it easier on the player to give names to the individual pieces, for their mental indexing.
The different sloped pieces especially confused me, they seemed hard to work with.
The work that went into this is obvious, I think the concept is solid, and the greatest task to improve it will be to tweak the user interface to work with the user's minds.
I especially like the way you went beyond lego, allowing for floating pieces, for transparency, and I absolutely love the blobs of light. With a very detailed interface, I could see someone much smarter then me creating s three-dimensional object with only those light blobs.
You should be proud.