The AI is pretty terrible IMO, it really doesn't seem to know wtf its doing half the time.
I actually kinda miss religion, nothing quite like starting up a good old holy war
Culture in Civ5 is a bit rubbish in its current form, to get it in any decent amount you have to limit you number of cities to a small handful, spam out wonders to get boosts and you still have to farm cultural city-states to get a decent amount. All the while pretty much gimping your development in areas like science and gold (unless you get lucky and start near a load of gold sites).
I do however like the fact that any unit can now travel over water without needing navel transports, although it would still be useful to have the as an option for when you want to provide some decent defense for them while in transport.
Im not too sure how I like the removal of stacking so far, while its nice not to worry about the stacks of doom from civ4 it does suck a bit that if get tech up fast you can pretty much wtfpwn anyone with a handful of units.