Not bad, nice and simple. I did start having some serious lag spikes around Wave 10. It looked like you might be triggering the garbage collector by calling 'new' too much.
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I managed to crash it by spamming too many snowballs, haha. I do like how you made it so you must be facing where you want to throw snowballs. That adds a bit more to it than just spamming snowballs all over the place.
It's fun to play, as far as stationary defense games go. It would be more fun to have more elements such as upgrades, more enemy units, etc. If there were more units I didn't see them as I only made it to wave 6 before crashing.
The "facing" mechanic takes a bit to figure out... I thought the game was broken at first! But I do like that you can't just shoot snowballs everywhere.
Well simple shooter with rather hard controls. I've got serious lags after while and I had to kill your game :-) You have probably some memory leak somewhere in your code...
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