Hey! Really fun game.
The controls are really tight and it's great that you can get better at it quickly.
So I definitely want to echo the letting people know when the freeze is up, either with a bar graphic or a sound effect.
So at first when I was playing I was holding Z all the time to cling to the wall, and even when the bar got all the way down, it felt like I would still slide slower and in a few jumps I'd get plenty of power left to cling. It felt odd. I read your comment on here about how you are supposed to continually jump and only hold Z when trying to make precise jumps, and playing that way felt a lot better. I think there is a way to make that more intuitive for the first time playing. I think if it worked more like you can use the wall cling for a set amount of time (and a smaller amount of time), then it expires and it gets put on a timer when you can use it again. (Like the carrots in Ocarina of time, if you use all of the carrots, they get put on a timer and they all refresh.) That way it's very clear that you aren't supposed to wall cling all the time, and it will encourage players to save it for when they need it.
I honestly kind of discourage the store idea, it could be fun to get a new character or something, but I think changing of levels and variety of the gameplay would be more effective. Maybe if you beat a level then you can start off at the last level you were at. (Check out super hexagon for example, survive for 60 seconds, you unlock a new level, but can still compete for a high score on any level.)
That's another thing that would be awesome in this game, leader boards!
Definitely a fun concept and well controlled. Good luck with it in the future!