you got something here but...
I hope this is unfinished. I see a lot of potential in this so maybe i can offer some stuff that could make this game better than the rating it's getting
1. add a pick your language buttons so you can widen your gaming audience
2. music of course. i think it would be interesting if had it when one starts to play a part that music part starts as well in the main audio, like drums start the drums in the the music start, guitarist starts the guitar part starts and so forth but make it to well it's the first one who start the attack starts the track and the 2nd doesn't do anything to the sound. be cool if you could pick what style of music you play as well. this all can be done if you just get the music unmastered with each instruments in there own tracks. can help you on that if your lost. (the music part not programming that is)
3. more variety of people on both sides, like a singer, keyboardist, turntables, etc. and maybe different enemys that go side to side and some fight back like the country singer looking dude plays his own against you. or crazy groupies that run really fast at you.
4. more upgrades (cause what's a drummer without a bass drum or guitar without his pedal board ) and more levels instead of just one endless level.
5. lengthening the line a little bit so you can see them coming.
overall like the style, graphics, and the idea of it. just keep working on it. hope to see the finished product soon to give it a better rating.