Good foundation
I can see a lot of potential in this game, things like how the pathfinding AI improves with each wave, and enemy behaviour changes.
At this point, it seems like you would benefit from getting an artist on board to help with sprites and design. A lot of people are going to be put off by the graphics, as the gameplay seems a bit jerky and it can be hard to understand what's going on with the simple graphics at the moment.
The same goes for sounds. It took me a while to work out what the timer sound was, and the gun sounds can get annoying and repetitive.
These things seem minor, but they can help improve a game a lot.
As far as gameplay goes, this reminds me a lot of Babo Violent (a free game floating around, google it), with the same top-down shooter style. Maybe that could help you with some ideas.
That's all I can think of, hopefully it helps!