Well are you going to tell me any of them? You have the chance to review the game, so do it, tell me the many problems with my game everyone else (Minus one guy) could tell me what issues they had in one post, I see no reason why you wouldn't to tell me the problems right now.
My responses to your problems are down below, but I must ask you why this game dissapointed you?
For the hitboxes if it's for the buttons then I understand, if it's for the characters hitboxes, it has a capsule to fit as much of the hitbox to the character's sprite to be accurate, maybe I should have made it a bit wider but I think it was fine.
The low jump is intentional, alot of the levels take place on one screen like your game, If every character had a high jump, what would be the point of Squarington's (aka the box) ability? He would be useless if every character could jump high would he not? Squarington jumping ontop of other characters would be a cool idea to use I will admit but most of the time the puzzles were designed so another character can reach a high place and then use their special action, maybe when I work on this game in the future I'll work on that.
Jumping with the I key was a choice I made because that is what I am used to in computer platforms, I will admit that space bar, up arrow, or the W key would have been a more conventional place to use the jump function
I also admit I should have let the player have some sort of hint as an optional setting instead of letting them figure it out for them selves, but I think the mechanics are easy enough to figure out without text.