Alright well as it is this game is of course very barebones but there's a solid base here. I'm guessing you probably had more variety planned but it fell through in the end?
Lots of small things could be added to make it more engaging, different enemies, different guns to buy you know, standart tower defence game stuff.
But even still, the game works well and runs smooth. And I personally also love the 8bit music style! So not too bad!