Well presented, lots of variety in the kinds of blocks you could use, and a really cool concept. Like some other commenters said, I felt like the degree of randomness made it a bit too much work sometimes, and that maybe a good middle ground would be a level with most of the pieces already in place and just two or three blocks you need to slot into the right spot. This would probably be more restrictive level design than you want, but players are clever and I'm sure new ways to clear levels would emerge even from that sort of level design. Still really good job!