TLDR on topic:
If I could change the AI I would... (I'll try not to be redundant and repeat what has already been mentioned, such as AI using switch mode)
1. Not allow units in transport (or Artillery) to move adjacent to enemy ground units UNLESS they cannot see the unit. (AI trucks SHOULD drive up and even get ambushed by player units hidden in Fog of War or hidden by bad weather)
2. AI should pay a little more attention to its supply status. A 1 or 0 ammo unit should probably not advance towards the enemy, it should want to resupply or even move away from the enemy if it cannot resupply. Currently, a 0 ammo AI unit on attacker will sit face to face with the player, becoming something of a roadblock that can be ignored.
3.
Also:
Currently, the order of operations goes something like:
Activate, move, fire all recon units.
Activate, move, fire all tank units.
Activate, move, fire all infantry units.
Activate, move, fire all artillery units.
Activate, move, fire all anti-tank units.
And so on. There is some variation to these behaviors (sometimes artillery will fire on a target before infantry attacks it) but these tend to be the exception not the rule. For example if you put 3 AI tanks and 3 AI infantry in range of a player controlled victory hex city, the 3 tanks will all activate first and move adjacent to the city (they may or may not fire depending on how good of a tank they are) and THEN the 3 infantry will get their turn to act, which leaves them blocked and unable to reach the city hex.
Sometimes this behavior is great and we want tanks to lead the charge as advance units. Sometimes though, we don't, such as the city example above.
Solution: When we configure units in the editor, add an OPTIONAL parameter called 'priority'. Adjusting priority, which is a simple number from... 1-10, moves up or down the priority in which the AI will active this particular unit.
If priority field is ignored, AI will active in the current order. Any number 1-4 will activate in advance of the typical AI order. A priority 1 unit will be the first thing the AI picks to move/attack with. Any number 6-10 means these units move even later than the normal AI decision making progress. A priority 10 unit will move absolutely dead last.
4. Add kamikaze setting to AI parameters. Similar in every way to attacker, but kamikaze will even attack when the odds are absolutely NOT in their favor. 10-0 attack? Do it anyways. A few of these units would be nice to keep good pressure on a player, and also fight against AI traffic jams.
Off topic thoughts:
After so many, many scenarios, I've grown rather fond of the AI for the most part. I'm not particularly sure that a more threatening and cutthroat AI is in the best interest of the game either, especially when it already exists.
For example, the AI and dealing with escorted tactical bombers. As mentioned, this pretty much never happens. If you escort your tacticals, the AI fighters ignore them because the attack odds are so dismal. Sometimes the AI will attack anyways though, but this is mostly because of Manstein difficulty setting. I don't see a problem.
Players on the average difficulty settings are rewarded for good escorting of their tactical bombers. Players on the highest difficulty setting run the risk of losing them even though they put together escorts.
If the AI intentionally soaked off fighters to absorb interception and then pounced and crushed player tactical bombers, I'm just imaging how players would feel losing their veteran units to the textbook example of 'zerging' and how they would ask 'why bother having escorts.
Also, if you create an AI that is immune to being ambushed and intercepted, all it creates is the illusion of a cheating AI. A player who understands sight rules and carefully places a unit in sight range of the enemy but keeps the escort out of sight should be rewarded with an intercept or ambush. I'm pretty sure if the AI never got ambushed and never ate a bad interception, players unfamiliar with the game would think it's cheating with some sort of Fog of War cheat. The fact the current AI does not cheat is exactly why it ends up in these bad situations. So you see the obvious problem with changing this.
Bottom line, a lot of suggestions seem to want the AI to play more like a human player. I don't think this is good at all. AI play and multiplayer are two entirely different modes of game play. When you play against the AI, you can expect to have a K:D (Kill:Death) ratio of 10:1, or maybe even better especially on the lower difficulty settings. You will never see that in a multiplayer game unless one side is completely crushing the other (the worst and most unfun kind of multiplayer experience).
Multiplayer is the place to go if you want an adversary who is witty, crafty, deadly, and ruthless. Singleplayer's priority is campaign play, and campaign play is fundamentally based on two concepts.
1. You should win, and win a LOT (or your campaign won't continue for lack of prestige/because the game is over).
2. Your units need to survive for extended periods of time.
Both of those tenants are in total conflict with the multiplayer setting of 1 piece battles, but that's fine. Why make singleplayer more like multiplayer? Just play multiplayer. It's like there are two games in one.
