Got to level 10, it was relatively fun even with the simplistick graphics. You could easily tell what which kind of cube does, which is nice.
The attack bullets could be bigger, they dont have much impact this way.
Sound affects were simple but servisible.
The shop was nice, but it didnt have a lot of variety.
Most importantly, dont force the player to pick up coins manualy, have them get magnetized to him at the end of the wawe, otherwise you are just waysting his time >v<