Finally got used to all the controls and managed to beat the first level. Then I wandered into the "delete save" portal, not knowing what it would do.
Mouse controls kill this game. I think you've got a pretty good start, though, and I do love 3D physics (even in Banjo Kazooie: Nuts and Bolts). The trick I used on that first level was to start the blueprint off at my destination using the scrolling, and then build towards myself. Obviously it's good that your green block cursor is always connected to the existing blueprint, but how come it can go diagonally from the blueprint when you can't place blocks there? And the game only responds to shift and ctrl on the left side of the keyboard.
You should be able to move the green cursor block with the keyboard. 6 keys for six directions.
I found myself wishing there was some way to return to the hub from within a level.
I think it's worth continuing, but definitely make sure you add sound!