The game concept is definitely very intriguing and different from other tower defense games I have seen. Being able to build your own environments/paths is unique and I like the variety of towers allowing for more strategy development from the player. One critique is adding different backgrounds to the grid for levels. The UI for the game is done well and is very clear with what you are purchasing and what each tower does. You can also possibly add more enemy types and enemies that have special requirements or features.