Bust A Groove. It's what got me into music games and I still consider it one of the finest. It had actual CHARACTERS with DIFFERENCES and a degree of actual CONTROL over the on-screen action on top of fantastic presentation and a great soundtrack!
However it always had ONE major flaw: You input the Dance Command on the first 3 beats and then hit the enter key on the 4th, but you don't need any sort of TIMING for the dance command. Let's fix that.
How? Well we make a note chart denoting where all the beats and notes in a song are and HIDE IT. NEVER show this note chart EVER. Now, when you input your dance command, if an input happens to line up with one of the notes on the hidden chart you get bonus points. The more you can line up, the better. HOWEVER! Nailing the notes is NOT required! Why? Because it would be all too possible for you to get a dance command that is too big and not enough notes to do it in on top of the fact that REQUIRING you to hit the notes would be too damn mean. You're already getting bonus points for hitting those notes, so you WANT to AIM for them anyway.
This completely changes the paradigm of music games, relying on musical skill and rythm more than lightning fast button inputs.
As an extra twist I'd bring back and manual branching dance trees of Bust A Groove 1, but rather than just letting players pick freely, high scoring moves cost "Momentum". You'd have a Momentum meter at the bottom of the screen. Some moves would give you few points but lots of momentum while others would be high scoring but COST momentum. Also nailing those notes gets you momentum as well. Oh and yes the branches wouldn't even show up if you don't have the momentum to pull it off and I WOULD like there to be up to 3 different dance moves you can do via the branching dance tree (as opposed to 2 in BAG1).
Wanna really up the ante? Custom characters. Let me make my own character and dance them against the Bust A Groove crew, learning their moves and allowing me to customize my dance tree adding a degree of deck building strategy to my music game.
...
...admittedly I don't think anyone besides myself would actually buy this game and lord knows it's too damn complex for most reviewers to understand. It's amazing how much music games have devolved since the good old days.
So ALTERNATELY I'd also accept just calling up Namco and having them make a We Cheer 3 only remove the Cheerleading theme and make it a straight dancing game. It's about the next best thing really. (No seriously. We Cheer 2 is awesome!)