Seriously. I've played three games on hard difficulty and got thoroughly beaten twice. Thoroughly meaning I didn't really stand a chance. Once I was able to siege Rome successfully and captured it on turn 19.
I'm not seeing the small one or two legion armies making suicidal invasions any more, so those easy kills and promotions are history. Overall, the AI seems to be doing a better job at concentrating its forces and making it really hard for me to surprise it. I made a couple of mistakes, and if the hard level AI wasn't exactly forgiving before, now it eats me for breakfast and then goes on a killing spree.
If you're tired of your typical helpless AI opponents, give this game a try...
"But here we are in a chamber pot, about to be ****ted upon."
-French General Auguste Ducrot before the Battle of Sedan, September 1870