Quick tip while it's on my mind. For the audio of the gunshots, add a tiny variation in the pitch for each shot so it doesn't sound so static / generic. Just a random.range(0.95f, 1.05f) and that'll do wonders.
There's not much to say, it's a solid little tower defense game, and the sniper + reloader combo is a bit overpowered. Definitely good for a weekend game jam that's for sure.