i thin that you should add some more bosses and some more upgrades to make the gameplay last longer,and you should also add some kind of background or story to make the game more interesting.The game gets a bit boring after a while because you are using the same moves over and over so i think you should allow the users to pick a class such as archer or mage or whatever to make the game more fun.but as it is now its a good 4 to 5 hours of fun gameplay.