My campaign setting was VH/VH.
I would say that AI activity increased since my last playthrough in 2.35, this might be the result of the increased movement range that armies have, a surefire plus. I was pleased to observe active Carthage, it took Sicily and native Numidian lands close to Carthage proper, leaving Numidia with one settlement in the Algeria. It was also in a war with Rome which took Corsica from it, but in the 47th turn Carthage had two decent sized stacks on Corsica.
Besides Carthage, Iberians were having a blast too. The Lusitani had three provinces in Iberia and they also held Morocco, while the Arevaci held the rest of Iberia plus western Gaul. Awesome.
Gauls were their oldselves, the Aedui held additional two provinces in Normandy, while the Averni haven't expanded at all. However, the Boii were saving Celtic honour, by the 47th turn they held 6 regions in central and westen Germany. I have never before seen this active Boii, excellent. They were winning their war with Suebi, which was three province faction, but were actively sieging additional 2 rebel held regions. The Lugii was 4 regions function in Eastern Europe.
Greeks were in the usual three way war, where KH held Thesalia, Macedonia held Corinth and Aitolia, while Epirus held Sparta. Epirus, probably through revolt and conquest, held Taras, Rhegion, Capua and Luceria. Needless to say, Rome was a big bummer. The team should seriously look into the Rome, and when controlled by the AI, make it menacing, the end game opponent that would offer a player the challenge in the late game, like the Mongols in the Stainless Steel.
My campaign however, started easy and turned even easier at about turn 30. At turn 47, I've held 10 more settlements, taking Seleucids to 33 settlements. This all makes me 15k per turn ever since turn 30. I would like to stress that I wasn't blitzing, each army contained only one general unit. I suppose one can not expect a hard campaign with a faction which starts with 23 provinces, still the menu lists Seleucids as "very challenging", it should be changed to "easy". What really surprised me was the speed with which Seleucid economy came into the positive (5th or 6th turn) and stayed positive throughout, though I was selling map information for about 1.5k.
Unfortunately, In my campaign CAI wasn't aggressive, Ptolomies especially. Namely, Pt had full stack near Side which didn't move to relieve the siege of Halikarnassos by me, even though it had enough movement points to do so. Eventually AI transferred that army (led by the FH) away from conflict via sea to Egypt. If I exclude the scripted siege of Damascus at the start of the campaign, Ptolemies haven't mustered a single offensive action against me, but they asked for ceasefire 5-6 times. There were two fun sieges against Pt, Akko and Alexandria. Also, it appears that possibility for general rebelion is pretty damn high, Ptolemies lost three general led armies to rebellion including army that spawned following my capture of Akko.
Nabata, Armenia and Parthia also at one point declared war. Of those three, only Nabata was aggressive, that is sued for peace only after I've defeated their sieging army, while at one point Parthia was sieging three of my settlements, asked for ceasefire while still sieging and when I refused simply retreated. Armenia never mounted a serious effort at all. The lack of AI aggression and high rebel spawn rate influenced my decision to quit the campaign.
Still, there are improvements over previous version: AI vs. AI is more active, javelins do look more effective, the mod team slowly coming to terms of changing the size of cavalry units which at one point I've suggested, sieges when there is proper garrison present are real fun.
The lack of faction in the Balkans is highly observable, since I would like to see Kushite faction introduced and apparently Belgae is reserved to be added I would solve the Balkan faction either through switching Aedui to Scordisci maintaining the number of Celtic factions, or switch boring Hellenic faction of Pergamon into Illyrian one.
BTW, shouldn't Antocheia Margiannes and Antocheia Arianna be named Alexandrias?
If I have enough time I will tryout the one settlement faction to see what my experience with it would be.