Really cool concept! Loved the puzzle aspect of managing the size of your healthbar and using it in world for both movement and interactions, it's really unique and works very well.
There were a few "gotcha" moments with buttons I wasn't expecting that I found made me laugh- reminded me a lot of old flash games where devs would kill you because it was funny. Particularly enjoyed the button that raised part of the zipline as I was returning to the goal (think it was the third level?)
I found that there were some issues with collisions - hitboxes felt a little unforgiving, and with the health bar moving instantaneously with mouse movement it felt tricky at times to tell how it would respond with physics.
Would be really interesting to see it expand further - would love to see you incorporate more UI elements into gameplay!