Playing my second full game, on a Highlands script so I'm afraid all your naval enhancements are going to waste. Immortal difficulty. I have several observations, compared to vanilla:
1) The AIs are better at teching, and much better at building wonders.
2) I have found it somewhat easier to maintain good relations with the AIs. This may just be due to a small sample size.
3) AIs are not particularly better at fighting. I've seen lots of strong units, like Stygian Guards, moving around seemingly randomly, rather than defending in cities or counterattacking. I haven't had any catapult or magic AoE spells used against my attacking stacks.
4) I just captured the Lanun capital. It has a Pirate Port on a lake, but could have had two more pirate ports on ocean tiles, and built neither.
5) The AI is really good at pumping culture in border cities (maybe this is just because OO was widespread in both games), and likes to plant a city right against my boundaries and then complain about close borders. I remember similar behavior in BTS, so this is probably not new. The Lanun walked a unit completely around my nation (from 12:00 to 7:00, with my empire as the clock face), and built an isolated city. Then they pumped 5-6 OO disciples into the city for cultural pressure. Cute, but not really an efficient use of hammers (espcially because I captured the city later).