Game loop is solid that is for sure.
Pixel art is also prettyy cool (I really like the sumbols on the green tiles and main character ofc)
If you make a pixelart game you should stay consistant with it in terms of pixel size in every sprite and all of the UI elements should be in that style (buttons and font are smooth).
Also the UI was not very intuitive, for a long time I didn't know that I can buy upgrades because I thought the next/prev buttons were for towers I will unlock later - So instead of next/prev you could go with named tabs like 'Towers', 'Upgrades' etc.
Game need some more polish like VFX and SFX but the core loop has potential.
Good job!