Nostalgia wave right here.
The biggest issue with this game is that it will become impossible around level 40-50 if you don't have the right upgrades/spells. The only magic spells you will ever need (besides nuke) are Insta-kill and flame ball. Another tip is to not get the auto-save feature, you could potentially mess up by buying a useless upgrade and never have enough money for something else because of it.
I haven't seen anyone else mention it on here but I'll say it now: The main stage theme is the boss theme from Turtles in Time on SNES, a good choice but it gets repetitive sometimes.