Expert is the hardest difficulty (except on drums, where Expert+ is the hardest) in the Guitar Hero series. Using all five fret buttons (or all six buttons in Guitar Hero Live), the note charts try to mimic actually playing the song as best they can. Several songs on Expert have such difficult note charts that nobody has been able to Full Combo.
Gameplay Elements to Make Expert More difficult than HardEdit
While Expert has no extra fret buttons, the patterns and note charts can still be much more difficult than Hard. Expert can also require an advanced technique known as Tapping. An excellent example of songs where tapping makes the song much easier to pass is "Through the Fire and Flames". Expert also uses more three-note chords than hard. Due to Neversoft's desire to make the game "more like playing the real guitar," three note chords are used in nearly every, if not all, of the songs on Guitar Hero III, and are used heavily in several songs ("Before I Forget" and "3's and 7's" are good examples). One new chord which is a 3-note split chord and there are only a few songs that use 4 or 5-note chords ("Joe Perry Guitar Battle" from Guitar Hero: Aerosmith, "Master of Puppets" from Guitar Hero: Metallica, and "Raining Blood" from Guitar Hero: Smash Hits as examples).