I have to say i have only done some Scenarios so far. First impression: Mongols is a little more challanging than the average scenario Civ has out of the box. Though i think i had a bad stratagy.(burn all cities to the ground save none...no infasturcture only works for the first two or three countries you wipe out) The Vikings scenario is less challaging but a lot more fun...I dont know theres just something about being able to ransome cities. I loaded up Rise of Rome but the way they screwed up the shape of Italy and Greece was disappointing. I have yet to play them though and they could still prove to be quite fun.