I think its okay
Its pretty good... I actually found that it was way too easy I got to like level 32 before i gave up it... at that point I was getting one shot kills if i felt like shooting... the mines i would buy every time made it more like a screen saver than a game... I suggest you go back and check your equations... keep the variables from getting too high and making soooo much money in later levels.
So overall could be better just make it get harder as you progress in stead of easier.
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