I just got done playing my first Warlords game, and I was thoroughly impressed with the AI. I played a noble game to get a feel for Warlords, and from what I observed:
- The AI could have scores similar to mine. In vanilla noble games, the AI's scores never even approached mine, but in this game two eventually overtook me (which lasted from the industrial era until I completed the spaceship). I think it was because they both had vassals under their control (whereas I had none), but still...
- The AI uses tactics in wars. I was on an island, and Isabella declared war on me. When my navy on one side of my island defeated her galleons and frigates twice, she attacked from the other side - a much further distance for her. My navy was weaker there, but I held her off.
- The AI doesn't build cities in ridiculous locations (most of the time). On my island, there were a few tiles on the coast that were not in my cultural borders. In vanilla, the AI would likely build a city there when there was nothing else, and let it be a drain on their economy. In Warlords, no one did.
Basically, the AI is much more intelligent in building its infrastructure and in fighting wars. I'm probably going to play noble again just to get a better feel for the AI.