Going straight from Beyond the Sword into Civ 5 really highlights their differences, and I've become so used to BTS that I find myself a little nonplussed at times in 5. Finished my game on Warlord comfortably, thought I'd step up to Prince...and it was no trickier. I feel the changes have made it more difficult for the computer to wage its familiar strategy of expand endlessly whilst maintaining a huge numerical troop advantage.
I'm not the greatest civ player ever, but I play noble on IV and normally dominate culturally, technologically and, eventually, totally. I get the feeling the AI struggles wearing down the redesigned cities, little fortresses that they are, but I miss building swarms of villages around them to boost your income AND I dislike that your tax income and research output have been divorced (and where's espionage gone?). All in all, it's a good start, but it lacks the smorgasbord of content, tweaks and details that expansions, DLC and mods have given Civ 4. And there's never enough aluminium to go around, why can't I build my tanks out of iron? (and pull them with horses?)