From a programming point of view I can see why someone would be wary of delving into things, because as soon as you start you become the "AI guy" and suddenly every complaint about how the AI works becomes your responsibility.
on the flip side of the coin, the AI would be exactly where a really good coder would make his skills shine. That said, some gripes with the AI aren't a result of bad AI code, but of messed up CTH calculations. These gripes tend to dissappear in OCTH.
As for my own game, i made a playthrough to test as few of the less silly Features. The added Ja1/DG Mercs have good looking face animations, but the speech selected from ja1/DG to be used in Ja2 often doesn't match the Situation at all. So when it comes to those mercs, the question is largely which of them are less cringeworthy. That their loadouts often don't quite work is a minor detail considering there's what, 4 or 5 loadouts per merc? Traits, Backgrounds etc. absurdly overpowered makes some mercs very useful (almost a requirement for certain things). For example scouting, spy and Radio Operator are IMO dubious as skills/traits. Is it really completely impossible for a seasoned battlefield Veteran to use a Radio set? Or to avoid being ambushed from an opposing suad whose Location is well-known down to the exact number of enemies? And what super Special Attribute it requires to wear enemy clothes to disguise yourself is downright bullshit. These skills should improve a merc's ability to perform these Actions, but as requirements for the use of this feature, they're absurd. And they're not even the worst skill/trait balance-wise.
For an official "stable" release, the number of bugs is astounding. The bug when mercs jump into a fence instead of over it is ages old, bugs relating to interrupts are ages old. Then, AT weapons seem to have been super-nerfed, not without causing bugs. "Ambush" Features is super buggy and had Ja2 freeze up time and again. Food system is bugged, even if I play without that system, some npc's will drop shit tons of food items. Enemies fleeing the battlefield can still enter a sector held by the Player, not without causing bugs of course.
But in the end, some weird "helicopter data corrupted" bug has ended my game.
Still, the bugs aren't the worst thing. The changed random number system goes too far for me. Almost every aspect from the tactical gameplay has become so super random that it annoys the crap out of me. Every time a merc misses i just know i could reload N times until he critically hits and kills the enemy. The old random number system was way better. And guess which change isn't optional...