Ai

The main thing everyone hates about the AI is that your allies keep there Generals in the city. I have played a few times but not as much to be sure with Glory of Generals 3

It's still a big pain in Army Group mode since AI usually got stuck by the surrounding allies. I think one of the main problem is the fact that AI cannot move pass friendly territories like the normal Conquest mode.

Agree. That is actually what I usually do; keep a strong enemy locked until I am ready to take it on.
But it's still a kind of bad to see a huge friendly armies got stuck unable to take Copenhagen.

AI looks overall smarter.

In campaigns, you will rarely see some unit doing literally nothing. However, there are more triggers and forced behavior than before (for example, this group of units upon this enemy general being killed, march on this city), which I guess is good for campaign, as it will avoid AI often thinking on its own, sometimes doing weird decisions . However, this also occasionally creates very aggressive behavior, like fast units going too deep and artillery sometimes charging to the frontline rather than stay static if they can already attack. I don't mind this, because they do serve as good cannon fodder for your troops, that are expected to be the ones doing the heavy lifting on missions. They also hesitate way less on capturing your own buildings to reach their objective, which although it pisses a bit, I guess its good, although I wish more intelligence from them, like they won't purposely send an infantry to a city or tank to capture a factory, its a bit luck based, and if it happens, it's when they will use those coins to add an extra troop to it. They should be a bit smarter here and infantry prioritize a city to upgrade amount and the rest on factories if possible and they have spare coins (which I guess they often do, as unless given an airport in range of enemies, they won't spend). On the other hand, enemy generals defending cities are sometimes static on factories meaning they will sometimes just heal or upgrade.

On army groups, them often hesitating to attack, preferring to play defensive and while also not really using forced march, or offensive airlifts means they will not advance and be blocked either by you or some stronger allied army group. This will sometimes get them blocked, which sucks both if it happens in your team and if happens on enemy team, as for the former, you will have less pressure pushing on other fronts while on the latter troops will keep on stacking and accumulating until you make a breach, which you will have to fight a bunch of bigger armies because of this blocking (and the longer you take to "free" it, the bigger it gets). They do also train troops all around their territory, not in the frontlines, which is not smart either, but this also makes it easier for the player when fighting enemy.

On United Front however, they are quite dumb. Both allies and enemies basically have 2 ways of behaving, either charge at you or they stay static until you enter their trigger range (normally their attack range or attack range +1). This is the most boring mode IMO and also the less rewarding, but I like them trying new stuff like this or army groups, but I'd rather have some other new game mode on next patch rather than more of this.

Sometimes good sometimes bad
Example
When I was testing strategies for my guide from Finland 1941, the AI ​​of the Balkans was terribly destroyed by Yugoslavia and I had to take half a map because the Germans also could not against it and in the second attempt it was defeated at about 20 turns