This is a very, very good start! I am very happy I gave it a try.
Just brainstorming an idea (you likely have plans along this vein already) is perhaps some sort of power ups? Either have like a "buy" system between levels or have targets in the blue block gaps with power ups, for example.
Some ideas might be you could have some to slow down time or create temporary invulnerability or just bust through a layer of blocks. Perhaps some that were innate and some that are user triggered.
 "Box Drop Demo"){kind=icon}