As for my strategy: You have to focus your upgrades on a few spells early and not diversify too much (just go for 2 elements, I like lightning/earth since not many creeps are immune to them early on) completely max the two elements you choose before going for the other trees. Only worry about 2 limits since you probably wont have enough crystal to max everything (again I went with lightning/earth) Easter Strike is probably the best spell, I never removed it since it does good dmg and holds enemies at bay.
I wouldn't publish a non-working game unless there was something specific you wanted feedback on. You can upload it and test it out without clicking publish.
I'm working on a racing game too. I've been tweaking the controls alot. It's nice to implement as realistic a system as possible with acceleration and friction etc... but past a certain point it feels less 'fun'. Nice start, I'd suggest some kind of bounds testing around the edges of the screen.
Decent, simple, nice look. Kinda boring, sound would be nice and maybe bonuses (time stop, temporary wall to stop the balloons from getting to the spikes, etc...) and more balloon types (maybe a slower one that takes two hits to pop) 3/5 for now.
Changed the enemy behavior. Moves faster now but only moves to get the ball when the ball gets close. Let me know if it's still too easy and I'll give the cpu more time to move towards the ball.