About the level of play: there is a big difference between Noble and Prince. We usually test it on Prince as the AI is stronger and gives a better challenge.
There is also a big differance between Noble and Warlords.
On Warlord level playing England (Earth map), early game is easier (just) to expand. Managed to settle a city in France.
Also Wonders are easier to build, early on.
Then the same thing happenned, as on Noble - first France and then Spain delare war. They send mixed stacks of 10 - 15 units (impressive - Blake).
But because of the easier start - I survive the attacks. I did not on Noble - they captured London.
However in my warlord game. It is now middle ages and Spain (I have captured the Spanish peninsulla - the cities it still has are built in Africa) has become a vassel of the Arabs. They are sending a huge stack of 16+ horse and 10+ catapult towards my European cities (3) , each with about 8 units.
I am in for a rough time now.
I am top in score but only 5th in power out of 23.
So to Houman - please keep at least one level below Noble, for the less experienced players. Despite the reported AI Civ problems, against barbarians - by the more experienced players. It still is a challenge to us newbies - mid game onwards.
Afterall, those complaining about AI problems on lower levels can always move up a level.
Those that can not play well on Noble - should be given the option of moving down at least one level.
P.S. After 500 turns only ONE - AI civ has fallen, and that was in America.