I looked online recently to find out a few things about it....

-The guitar may have 9-10 buttons, I don't know the details, but they have decicded they are adding more buttons, =( (9-10 is the max)
-You can create songs of your own, much like how Grage Band (Or however the fuck you spell that...) But theres no singing for copy right purposes, =(, I wanted to make a uber metal song from Carry On My Wayward Son, =(
-Drums are very different if you havn't looked, they have simbols on the top now, 2 of em, its odd...
=l
-If you had no idea that there was other instruments, I'll fill you in, Guitar Hero is rock band, The thing I noticed is everyone is just going to play guitar and drums, so yeah
For More Details, Go To This Site!

http://guitarhero4.wordpress.com/

Also, These are the songs I requested to be on Guitar Hero 4, you can request songs also by going to the Guitar Hero 4 link at the main menu

These songs please!

-Thunder Horse - Dethklok, I know it was on 2, but, This song would be awesome to play as a band.
-Awaken - Dethklok
-Son Of Pearl - Endless Sporadic
-Push Push Lady Lightning - Ban Camero
-Lost - Avenged Sevenfold
-Bat Country - Avenged Sevenfold
-The Good Left Undone - Rise Against
-I am Murloc - Lvl. 70 Elite Tauren Cheiftain, I know, I know, But it would be awesome, lol.
-I'm Alive - Disturbed
-Map Of The Problematique - Muse
-Follow - Breaking Benjamin
-Cry For Eternity - Dragonforce
-For Whom The Bell Tolls - Metalica
-Dying In Your Arms - Trivium
-The Evil That Men Do - Iron Maiden
-The Truth Will Set You Free - The Flower Kings
-This Fire Burns - Killswitch Engage
-Welcome Home - Coheed And Cambria
-Holy Diver - Killswitch Engage, not Dio
-Winds Of March - Journey
-Master Of Puppets - Metalica
-In Peices - Linkin Park
-Scream, Aim, Fire - Bullet For My Valantine
-The Sound Of Truth - As I Lay Dying
-Black Bird - Alterbridge
-My World - Sick Puppies
-In Keeping Of Silent Earth - Coheed And Cambria
-Bloodrocuted - Dethklok
-Hot Dogs - Limp Bizkit
-Life Is Beutiful - 6 am
-The Running Free - Coheed And Cambria
-Beverly Hills - Weezer
-Pull Harder On The Strings - Trivium
-Hallowed Be Thy Name - Iron Maiden, This song would be awesome on Guitar Hero 4 and has deserved its place so many god dang times its not funny, this song is absolutely awesome and a must that you put in!
-Warriors Of Time - Black Tide