Great work! I really like these style of games. Not sure what they're called....survival RTS? But yeah, it's always fun to hold off insurmountable odds. I think you have a great base for a game that can easily be fleshed out into something more. At the moment, I do think the game is a bit too easy. Resource collection seems to snowball really quickly and repairing the towers probably shouldn't be instant since I found if I click repair as fast as it pops up then I almost never lose a tower.
Good job with your submission! Hope you continue with developing it!