Even though you pitch this as a multiplayer game, playing this solo had that tingling feeling of both sides of your brain firing at once! I never knew how much I wanted to play Tetris and a 2D platformer at the same time until now! It felt great to have the tension of the water rising close to you and having to solve block/platforming puzzles on the fly, and then being rewarded for a well-placed grab jump with a bit of breathing room (much like clearing lines in some upside-down version of Tetris).
Really the only things I would want to change is for the platforming character to have a little slower side to side acceleration (the movement is so snappy with kbm that I felt like I was constantly on the edge of running off blocks, possibly not an issue for controller), and maybe for the bespoke levels to have a set order of blocks (feels like sometimes you can have a good or a bad run of blocks).