Like the guy who plays Stepmania, I play it too and ITG and DDR, and IIDX etc.. You said you'll put in a option to configure keys, please do it asap, the game seems cool, but is unplayable(I refuse to play easy when I should be able to do the hardest difficulty.) when it gets implanted I'm sure it'll get 5/5 from most people.
Like in other games similar in the aspect of endless, it would be nice if we receive achievements for starting the next game, more money, cheaper upgrades, free towers, etc... Honestly this game is slightly boring but highly addictive. With achievements it would be fun and still have the high replay value