Early experiences on Emperor are not positive, with no real changes to AI behaviour - save, perhaps, a greater reluctance to retreat from winnable fights (or at all). This is less positive than it sounds - the AI remains much less aggressive and less capable of supporting large armies than Civ V, so it really just sends things into a meatgrinder piecemeal. It makes wars more of a time sink than they were, and that will cost you if you pursue it for too long, but the AI itself still isn't effective in combat.
Glaring issues:
- Garrisoned units still don't attack, and rarely switch places or leave a city when that's a reasonable option. Most of the time cities remain ungarrisoned.
- AI unit composition remains dominated by melee units for most civs, with a typical civ like Rome (my main opponent) having maybe an archer or two and a chariot, which will not be coordinated.
- Stereotyped targeting behaviour that doesn't change with context. For example, I was attacking a Roman city and had two nearly-dead melee units after using them to take down the city's defences. With its final shot the city targeted the healthy archer it had been exchanging fire with for several turns.
- Very little aggression when faced with combat modifiers. In that same battle I kept a scout at the flank of my damaged units. A Roman spearman adjacent to it never attacked, which would have incurred a river modifier, and also never moved to a more favourable position.
- The new 'never retreat, never surrender' behaviour prompted the Romans, at a couple of points, to stand a unit within range of my garrisoned archer and exchange fire with the city until the Roman unit died.
- Something that may actually have got worse over time, the AI seems incapable of adapting to a defeated attack. It will prepare its initial attack, then typically declare war and besiege the target city with enough units ... but if those are destroyed or the city retaken (if the attack's successful), it doesn't appear able to repeat this behaviour for subsequent waves - without a plan of attack it will just send units at you one or two at a time. It also won't usually move to reinforce a city under attack.
