Considering the fact I can't return to where I left off if, for any reason, I need to close/reload this page, this game is too hard. 

If there were any way to return to where I left off - round selection, save codes that put me back on a given round if entered, a cheat code to skip rounds - then I wouldn't mind the difficulty.

Lastly, I can't change my purchases using the round coins. My one purchase of a health upgrade has been a hindrance to me, due to my power struggles, but I can't change it to a power upgrade! [Also, if you were paying attention, being able to change upgrades would solve any concerns with returning to where someone left off; you wouldn't have to worry about what things coins have already been spent on, because what they're spent on can be changed!]

Also, their are some grammar issues in this game, especially around the first round.