Quite fun. I like how the game makes you utilize the unique properties of different blocks. I overall enjoyed the puzzles.
Some suggestions:
I recommend making block retrieval a separate button. It's very easy to accidentally delete blocks while trying to place them. Additionally, making it so holding RMB retrieves all blocks would be great. Sometimes the block drops out of range requiring a full restart. Most games bind camera panning to other buttons(MMB or hold some button+ move mouse).
Some levels require you to place blocks after falling for a long time which is quite hard to time. You can try adding slow mo while aiming. This'd also allow you to preview the whether you can actually place the block there which would be great. To make the player not abuse the slow mo, you could add a limit to it and restore it when the player reaches ground again. But it is your choice since it might make the game a bit easy(and lower the barrier to infinite static box jumping).
Overall it's great with a lot of room for expanding in the future.