You are most welcome to disagree with me
It's not a case of difficulty levels though. The AI really struggles with the 1UPT - they should be hiding their ranged units behind their melee but so often they do the opposite. They also have no clue how to use mounted units and indeed very rarely build them. They'll split ranks to chase down a worker or settler and all sorts of stupid behaviour making them easy to defeat. I'm not much of a warmonger or tactician but I find the AI ridiculously easy to outwit in battle, even on the hardest difficulty levels. While it's cool defeating an army twice the size of yours it's not fun when you can do it nearly all the time.
They also struggle with infrastructure in their cities. For example, I've seen countless cases where an enemy city has trading posts everywhere but will never build a market to capitalize on them. Stuff like this should not be happening in a game of Civilization's calibre. It's the sort of thing you expect in a beta, not a released game.
Diplomacy is the other factor I intensely dislike, though it's a matter of preference here rather than poor coding. The AI are made to act like human opponents, out to win the game no matter what. I thought this sounded cool when I first read about it but in practice it's not very fun as leaders don't really have the same sense of 'personality' that they do in Civ4. They're supposed to have unique tactics but to me it feels like they all play the same way. Very little of what you do in diplomacy has any real effect (except with city-states - which I do like a lot) and none of the leaders can be trusted. To me it feels like all my games are multiplayer games but against fairly unskilled opponents.
I'm not trying to turn people off Civ5, except maybe to say 'try before you buy' (if you can). It's quite different from Civ4 and has divided the community here on CFC considerably (see the main Civ5 discussion forum). My feelings are that Civ5 targets a much narrower range of players than previous versions did. Those that fall in that range love it and that's awesome for them, but those that fall outside, like myself, are disappointed.