Lots of fun! This'd be great on mobile.
Good sfx choices, soundtrack, and artwork.
The fundamental game mechanics are simple yet interesting, but it is very easy to snowball effect (I got pretty far just by bombing). Maybe increase the cost to place bombs. Being able to repair or upgrade walls would've been nice, but I'm not sure if that would've made the game too easy.
Hotkeys definitely help with placing objects.
If you plan on going further with this game, maybe introducing other player mechanics like melee, spell casting, dropping money bag to increase speed but is vulnerable to enemies, other types of objects/obstacles, etc. would make for a cool sequel, or for an entirely different game.