The game is basically a classic tower defense, game works fine. I would say that there is not much consistency and immersion, information like tutorial for how to play or at least tooltips to what the towers do would be nice. I also feel like there is nothing new going on which breaks into fast stereotype and breaks the gameplay, definitelly lack of feedback for player what is new etc. I would suggest to at least tell the player, if he progresses to a new wave, how many money you get for destroyed objects and also some basic rules on start of the game like "prepare yourself and defend your life" or smthn, maybe a short story what is happening. It is not very informative, what is this game about either.
I like that, there is on tutle screen the "gameplay" which gives you idea what you are playing.
Sound is not bad. Music inst bad too, maybe it changes too often, it is better to use one music track if it is better than four IMO.
Graphics, well it is there. Good thing is, it doesnt hurt the gameplay. Try to be consistent with use of font with the rest of the game, objects are not very distingushable from each other, I had also a hard tim identifying of what those objects are, use of colors is not good (try to learn some basics of color theory).
Hope it helps you to make better games, keep it up!
Try my creations on newgrounds or Google play, feedback highly appreciated!