I plowed the game repeatedly on normal->challenging->hard, but ridiculous had AI bonuses that were too stratospheric for me to overcome. I think it's probably beatable with a good random map roll that dumps strong heroes near you (or cheating by setting all the AI factions to your side), but not really interesting.
Haven't tried again since they lowered the AI bonuses no ridic, but really, exploiting the game is pretty boring at this point, I'm waiting for the AI revamp to try again.
Mostly at this point I'm just looking at bugs and design issues, or UI stuff that drives me crazy.