Your long blocks can pierce your square blocks if the square blocks are flipped to their sides. I felt like I wanted the pieces to topple, there is visual feeling like they were going to as I tried stacking them in weird ways hoping their weight would collapse them. I did get some to toppled over and lay diagonal. Some of the shapes get caught on the edges of other shapes and do not align to the grid. You can potentially block the entire play space by overlapping shapes in unexpected ways.
Maybe you could change the color of the bottom faces of the shape to show which section of the grid they will land on (which matters kind of less if you build up and don't see the grid anymore. When you click the grid to land it can be hard to tell which parts of the shapes are going to land on which part of the grid (dropping the long block after it is rotated to lay horizontal detects the grid drop at the 2nd cube of 4 in it's structure). Maybe highlight the bottom of the shape with a different color than its overall visual indicator of the overall shape? Also so you can see where the shape will land at on other blocks that were previously placed.
I built up high enough out of curiosity to see what the world looked like and I got to see the snowy mountain tops. I was surprised to see such a big world around the little play space. Kind of entertaining to me. I would add more random things to the environment (as looking at the world and wondering what I would find, was interesting). I really like the camera rotating with the right mouse button. I would have used this kind of control for my block mechanic game excluding the pausing of the time scale, if I would have thought to freely roam around on the rotation axis.