Stoopid brain! I don't care if you think a sandboxey sort of "Robin Hood in ancient Greece" game would be awesome, I want to stick with the game we've got going now. The characters have almost reached 12th level and it's time to start throwing the really crazy stuff at them! Heck, look at this weekend's session: two behirs, a green dragon, and a frickin' dragonspawn godslayer — how often do you get to throw an encounter like that at your players?
So stop flaking and stick with it. You don't need to be coming up with a new campaign idea now.