Short game, but certainly a lot of fun. The first thing I tried was seeing if you could stack bombs for bigger jumps, which I see actually is a required mechanic partway through "Spike Hell", which is nice. Makes speedrunning the game a sure possibility. (Also, there's a mechanic where you can fire a rocket off in mid-air to gain momentum opposite to where you shot, but only once before you need to touch the ground again; made skipping parts of Spike Hell quite easy.)
Like one of the other posters, I wouldn't mind a few extra features—some that are more QOL, or just to make the game a little more interesting, or even to give the giantess characters some additional life.
- A fullscreen mode would just be great in general, with maybe an option to play as normal, or zoom the level out away from the player character to see the full breadth of the level and/or giantess.
- The option to change the keys you use; my laptop's left arrow key is completely buggered (I do a lot of text editing), so maybe the ability to pick and choose between WASD / IJKL / arrows for each function, or just to customize your own key layout would be nice.
- Safer, but more complex maneuverability challenges—utilize the ability to "super-rocket-jump" more, and take advantage of the player's ability to fire in the air, perhaps blasting off walls to propel them massive distances.
- You mentioned in another comment the possibility of exploring inside the giantesses—what about just reactionary animations for shooting weak spots with rockets, maybe turning the giantesses into "mini"-bosses?
- Shoot the catboy(?) in the balls enough times and watch him recoil, revealing the way out of the level.
- Blast the grinding girl's nipples to turn them into bounce pads toward a secret alternative path?
- Maybe climb into a girl / boy and force an orgasm, making them collapse into a bridge across an otherwise impassible gap.
- To that end, a good and proper boss would be a nice way to tie up the game, maybe incorporating one or all of the interactivity features above. (Maybe the player is stuck on a plain wooden chair, and their SO / the character that shrunk them(?) is trying to crush them by crushing them with their chest and/or ass interchangeably.)
I think you've got the base of a solid game already, but there's so many ways you could advance and improve upon it. I'll be looking forward to seeing where the final product ends up.