Hello,
I have neutral feelings about achievements, but to some degree they can tell you if the game is really too easy, as many people claim. Here are the numbers from the global achievement list for completing the game on:
Settler: 16%
Chieftain: 25%
Warlord: 14%
Prince: 13%
King: 5%
Emperor: 2%
Immortal: 1%
Deity: <1%
Don't ask me why this does not add up to 100%
I cannot believe that it is because about 25% cannot win the game even on Settler difficulty. Maybe 25% of all players don't play while connected to their steam account.
But it does show that the majority plays on the lower skill levels. Without any deep analysis and by just looking at the above numbers, I would say that it looks like a Gaussian distribution centered at the Chieftain/Warlord difficulty. So, apparently, in terms of the a v e r a g e player the game is not too easy. P e r s o n a l l y, I find CiV much easier than Civ IV BTS. In Civ IV BTS I was never able to get past the Noble/Prince level whereas I can win CiV on King/Immortal (post-/pre-patch, and I haven't tried on Emperor after the patch yet).