I found a bug: if you pause in-game and toggle fullscreen in the options, it doesn't give you the option to resume the game anymore.
Also, I think the graphics are fine.

You
do get better at spriting the more you do it, but redoing the graphics for one game would probably just result in demotivation and headaches. I'd say something that is a lot more important than realistic graphics is
different graphics, so people can easily differentiate between your different characters just by looking at their unique shapes, and this game does that pretty well.
But I agree with qubodup about the mouse jumping, it should be fixed. The classic TD medals
might be fun too, but I think that a medal system works better when your units have a threat of death or deletion for more efficient units or something, otherwise your units just get indefinitely better and better as the waves get harder and harder, which works just as well as medals not existing in the first place.
EDIT: Tried the new version, froze at wave 24, but it's still pretty easy. I think that a good way to up the difficulty would be to perhaps make different units better at defeating certain enemies (i.e. engineers more proficient at destroying vehicles, maybe a future anti-air unit to destroy helicopters), and forcing you to remove some of your old units to put in new ones to defeat the enemies in the next waves. This would give the game a sense of strategy, and will likely trip up people who didn't think and make them go "huh, so I have to think" and then they'll go on to try to beat it again.

If you're going to do this, it might be necessary that you clue in the players on what to expect next. Since it looks like you like to send out mixtures of multiple different enemy units, a bar that moves down and telling you what enemy types to expect in later waves ala GemCraft would probably not make much sense. Perhaps you can give your waves witty titles and tell players the titles of the next waves so they can have a better clue as to what to expect, and they'll be more memorable so players have an easier time to associate their wave strategies with wave names than wave numbers, plus I think they'd be just cute.

A couple of examples of these titles are "Guns A'blazing" when there will be infantry units, perhaps you can give them guns and/or flamethrowers to fight back, "Of Tanks and Men" when there will be tanks and men. Anyway, these are all random ideas I'm throwing out there if you need some, I am by no means saying that your game would be better or worse with these implemented or telling you what to do. Just have fun.
