I just played an Inca game, and It was incredibly easy. I think the hardest would be Greece. No matter how hard I try, I just can't win that game. It's surprisingly hard being trapped between 3 potential super powers (Persia, Russia, Rome (Depends on the game for Rome, but In my game, Rome Prat rushed France and Spain, and vassalized England early.)), with horrible land. Even with the new UU, it's hard. Even if it is European, it's unique.
I suggest you at least play a offline game with them, if only to 0 AD or so. Just wait and see...
I accidentally voted for Inca, so subtract a vote from Inca and add it to Greece. >_> <_<