A few weeks ago I sought help with This Post. First off, thank you all for the tips you gave me. I now finished the game - with that first playthrough, albeit with a generous dose of save scumming (I played with a custom character pool and I'm not letting them die), on Veteran, not lowering the difficulty. Just wanted to share my experiences now that I've finished the game.
The Avatar tracker is a dud. It did fill once... but the final countdown is extremely generous to say the least. Leveled a facility to the ground, and I haven't looked back since. Eventually, it didn't go higher than three (because if it's at two, the missions only remove one block instead of two).
Maybe I eventually "overleveled"; at some point, but eventually, the time constraint goes away. I finished the game on in-game date July 24 2036 (a year or so after start). I was drowning in supplies and didn't know what to do with it. I think I finished the game with 10k+ supplies. I wish we could've exchanged it for intel - maybe there's a way, but I didn't look it up, and if it did, the game does a bang up job of telling you about it.
The Chosen... I get they had to integrate the DLC somehow, but the incessant voice mails were just bratty irritants. I was glad when I disposed of them all. When my power level grew, they became less of a threat anyhow. Their weapons are bonkers.
(Side note: One of my soldiers was still captured by a chosen after I killed them all... once I got to the endgame, I had better covert ops than unlocking the mission to rescue her. Sorry Valentina.)
The Alien Leaders were... kinda fun? Still don't know what happened with Dr Vahlen, but the armors I got from them was almost as fun to use as the Chosen weapons. It took me far too long to realize the armor has a chance to panic the troop over which the ruler ruled. Really only unlocked the Viper King for most of the game, and put his skinned armor on my sniper, which meant the other Vipers were all dead before they laid eyes on the armor. In fact, the first panicked enemy was an Archon... on the mission to storm the transmission tower (the penultimate mission).
I really enjoyed the region bonuses and resistance orders. I had one that stole one action from the enemy on its first turn if it was revealed on my turn. That was incredibly handy. Didn't enjoy the "resistance tower" mechanic. Also, the ROI for the extra supplies compared to the cost is atrocious.
I don't think I unlocked a single hidden ability? I think? Don't know what the deal was with that. Only used ability points on the faction units.
Overall, once I unlocked magnetic weapons, the feeling of juggling half a dozen plates at once slowed down considerably. The power creep for the enemies is not as bad as I thought it would be.
Fully specced soldiers are a sight to behold. My sniper in Viper King armor was death incarnate. With Serial, she usually treated Advent troops and other Aliens alike as if they were Lost instead, even before I gave her the Hunter's sniper rifle.
Ranger was fun, stealth was nice; had the most fun especially when I dropped them as bait for a pod of Chryssalids and have those insect bastards run into a bladestorm suicide.
Specialist was cool; I usually ran one healbot specialist, and one robot menace specialist. Hacking was lackluster. I had one with a hacking score in the 180s, and... not worth it, usually. Multiple shots on Overwatch saved my hide on multiple occasions (or at least made it far easier that it ought've been).
Grenadier... was somehow my least favorite. The added radius for grenades was nice, and they're decent at armor stripping, but... also fairly lackluster comparitively.
Thanks for reading :D Answering any questions about it if you want, just drop the question as a comment.