JamLegend - the browser based Guitar Hero
paulstamatiou.com
paulstamatiou.com
There are lots of Guitar Hero and Dance Dance Revolution clones in Flash, and while this one seems especially well made I still feel the whole thing is silly when you're just using your keyboard.
The physicality of playing is what makes these games fun and memorable: it's tapping your feet forward and left on a DDR pad or hitting sticks on actual drum pads or raising your guitar controller at a crazy solo.
Whenever I play these Flash versions (or even the Tap Tap iPhone game) I just think Hmm, I'm tapping my fingers in a pattern that matches these okay songs the developers found for free on the internet. And I can't move because my keyboard has to sit on my desk. This really isn't that fun.
I'm tempted to say the pattern matching mechanic is just an excuse to achieve the essence of the game, which is making people move. But that's probably not right because I recall PaRappa the Rapper on the Playstation was just pushing buttons and it did well.
So I don't know what it is that pushes a game beyond rote pattern matching into something fun, but to me these Flash clones don't have it.