While the art is definitely SBIg, there's some genuinely neat ideas in here!
The items turning into bonuses in the later half is really cool, and I like that you let the player stay and farm more if they want to.
I sadly never made it further than wave 8, the giant is just way too tanky for me even with level 2 cannons and wizards. I think some healthbars for enemies would've been a real improvement, as it was hard to tell if some attacks did anything. With the spells in particular it seemed like the enemies were unharmed until they suddenly died.
Also I noticed the sound is REALLY quiet, like I barely noticed the sound effects in the latter half until I had my volume up 2-3x what it usually is on my headphones.
And the main menu doesn't fit on screen at all, while funny it does make it hard to tell that the player is supposed to do anything at first lol.
There's definitely some balance and QOL features that could be added here, but this is a neat idea I think could be expanded on. Good work!