Ahhh, Forza. I totally relate to what you're saying about how it can get boring quick - but, Forza Horizon was absolutely amazing, especially the drifting. And the soundtrack for it was just awesome, found so many unique artists that are still a part of my playlist to this day.
I've never really been a fan of Midnight Club Racing - it just, eh, never really appealed to me. But, if you seem to be the thrillseeking type in games, especially with what you just described, why not Grand Theft Auto? Open world, great soundtracks, so much to do, etc - the world is yours in that game. I love me some GTA! @CrimsonClad
insta-bored with GTA, every time. Yet I loved Crackdown? Go fish.