I think the idea of Blitz...which is a downloadable/cheap game that doesn't require an instrument peripheral, yet utilizes the existing instrument tracks and social media...is pretty great.
Having played the game for a few hours...after three or four runs, it all seems the same. Just repetitive button mashing (which actually hurts my surgically repaired thumb) after a few minutes.
I don't think the game is bad. It just became quickly apparent that the gameplay is totally not for me. I got into Rock Band because I liked the visceral sensation of pretending to "play" music through the game and the co-op gameplay/party aspects, and that's why I'll continue to play RB3 going forward.