I spent some time the other week on it, played through a few games.
To the questions above:
Seemed as stable as base FFH2, at least I never experienced a crash. But it does have a lot of missing texts in the civopedia and sometimes inaccurate notes that refer to mechanics that have been changed (rare)
Improvements seemed fine, automating workers didn't crash my economy, but until the 1.1 patch capturing cities can nuke you a bit when you suddenly have huge upkeep due to lack of city influence. A few disciples creating art can help with that now, and to be honest most games I had a pretty big econ so it didn't matter anyways. I liked not having to worry about city building upkeeps, but I ended up building almost as many land improvements as vanilla, just a bit slower pace so its a bit meh. The finding new resources if you have the improvement is fun, esp with the world spell that increases chances to find things, but its pretty OP esp for big civs atm.
AI did seem smarter, esp in splitting forces to raid out improvements and starve cities. I don't play at a super hard level, but I didn't notice anything totally dumb.
Seemed compatible with any map type or generation script. I only really tried out the Erebus continent though.
I did find it interesting that with the split tech/ magic trees of research as well as the universal resources that you stockpile like stone, etc . .it actually felt a bit more like Elemental in those aspects. Its still a very different game but I did find it interesting how different teams of thinkers converge on similar ideas as what a good direction for a 4x is.
My biggest issue was just the labyrinthine understanding of different civ mechanics. I often felt a bit pigeon holed into a certain tech progression in the early game, get ABC to get these special units for your civ or get rolled by the AI . .and on the flip side getting a grasp on some of the later mechanics is made difficult by the layers of changes that aren't necessarily correctly documented, or are just plain missing. My civ needs to get Alric the ascended to level 15 to win the game? Great. Too bad I can't figure out anywhere how to recruit this unit, since it doesn't exist anywhere in the civopedia that I saw, what tech I would need, or anything about it. Or the Astrikah civ, who seemed interesting, but for the life of me it seems that one of the most basic and important abilities to the civ - souldrink- is missing, or hidden somewhere. Or the Sidar, who I would think that the creating haunted lands would be a terraforming spell now, but it isn't, and I still don't know why I get creepers that can create them, or why I don't . .etc. Just those frustrations in a 4x where you would like to plan a strategy but really can't because until you've played the civ for some time you don't know what the little hidden things are or what might be buggy or what the missing link is that the tech help doesn't tell you.
Still in the end its obviously a very extensive and thought out mod, and at current my favorite flavor of FFH / civ4. I'd probably love it if I had more time to figure out every little nook and cranny of the different civs, and play them multiple times, but as is, its a bit of fun to have. Still I find myself reaching back for a bit more Elemental now, which isn't such a bad thing.