I used to be a big fan of Guitar Hero/Rock Band. Both games really took the gaming world by storm with their unique and original gameplay. Both franchises also tried to up the ante every year in trying to escalate the game experience for the end user.
But now the franchises are guilty of over-saturating the market in a short time frame, and with not much in the way of innovative new gameplay, the fanbase has started to stay away from the newer releases.
Instead of being critical of how stagnant the two have become, I have decided to pitch a few ideas that might bring some new life to the games:
First. a major change in the key peripheral:

It features a sliding button panel which amplifies gameplay. Now the placement of the 'notes' adds another dimension. I also added a few more buttons for combos and specific notes, and the purple button is intended to mimic a 'Slide Guitar', which will act like another whammy of sorts.
The onscreen gameplay will look something like this:
(More likely to be in a perspective view)
And it doesn't have to stop at the guitar. Here are a few more ideas to help revitalize the guitar games: