Fun concept, kind of a take on an arena roguelike.
It could use a bit of work gameplay-wise, though. Enemy spawning ramps up way too fast and they can very easily box you in and prevent you from going back to the tower before you get many upgrades. That + the stack limit and energy mechanic makes it so the most efficient way to play is to stay out until you fill your stack of items and going back in as soon as possible. The player projectiles are also really small and don't have an outline, so they're extremely hard to see.
I think if you lowered the enemy spawn rate scaling and didn't have a stack limit, there could be an interesting gameplay loop of upgrading energy to stay out longer and longer to risk getting blown up to have a ton of resources to play with.
Despite that though, it's still really fun! It's definitely got promise.