I am Guitar Hero man as well, but you got to give credit to Harmonix their DLC beats GH hand down, some fantastic songs from Band I love. GH4 had slightly better soundtrack than RB2.
What I hate about RB2 is difficulty level, normal is very easy, and I can't play with pleasure all songs on hard some of them being fucked up.
When I play the most diffucult songs on GH3 or 4 on medium ( Crazy Train, Mr. Crowley, Soothsayer, Dragonforce, Trapped under the Ice) it's great fun , on RB2 medium is fucked, some songs on hard or expert are easier to play than songs on GH played normal.