This game was absolutely AMAZING, at the spike hell level i was straight up just having fun, i forgot the reward in the end despite acknowledging it was a thing.
I might just be saying this because i am obsessed with difficult games, but you should really make it so somehow there is more platforming and strategy with the giantess and giant in the first two levels, unless it was intentionally easy as some sort of introduction to them for future levels they'll be in, in which case, smart move, definitely do that too for any new characters you add.
Gameplay-wise it would be nice to make the triggerable box collider for the arrow bigger instead of making it exactly the size of the arrow, because i'd find myself behind the arrow when going too fast , and i'd have to walk to the arrow to go to the next level, it fits for the potion though of course since you'd supposedly pick it up, but for the arrow it's more convenient to have a box area around the arrow that teleports you instead of the arrow itself teleporting you. (this is really just an inconvenience, nothing bad or crazy).
Immersion-wise, it would be nice for the player to die according to the situation, for example when crushed by the giantess, the sprite could just disappear to represent them being crushed, seeing them fall off the map kind of ruins the immersion, and if you do add specific deaths, the player should definitely take longer to reappear, but from experience i know that to change the death animation for each situation is difficult and confusing, so i'd ignore this myself.
Finally, to add to the immersion, to play around with the giantess' colliders, since her body is completely to the side could be nice, maybe you could go a bit in-between her cleavage and ass since she is looking to the side (though i see you've been playing around with squishy body parts, so i'm guessing that maybe you're planning to use those instead?).
Besides these things, this game is amazing, i got so excited when i passed the second spike hell stage i was basically screaming internally, and everything looked absolutely gorgeous.