I've been playing the beta over the week-end on the Crimson Caldera story map, with an underground start, strife oathsworn and a dragon ruler. I'll post my impressions below.
Underground map generation
The location of my underground starting city was rather dismal, although that's not entirely unusual when comparing capital locations to others that can be claimed throughout the game. After claiming my five nearby resource nodes, the only path forward was to head towards the surface, through three empty provinces, into a desolate biome. There were very few fights, especially as the slow pace of digging meant my first army had to head up to keep finding encounters even before I cleared my starting region.
In addition, the caves still suffered the usual woes they have since the release of the game. Clearing my capital region meant moving armies away from both the surface passage and the two exits to other connected cave pockets. This is an issue that repeated, especially on a constrained map like the Crimson Caldera.



A picture of the cavern to my east, also shockingly empty:
The lack of roads in the tunnels I cleared, as well as their length, made the underground largely inhospitable to armies. The new map generation creates very long tunnels: I dug through five provinces to get to another pocket, that passage is simply not usable in a realistic scenario. Picture below, the road was of course not present before I placed it.
These tunnels were made of Ashlands, which my cave-adapted armies did not care for; despite this, my spider auxiliary fell behind. This is a recurring concern with biome adaptation traits. Now that the Item Forge is thoroughly integrated into the game, I'd like to suggest adding an item infusion that grants Cave Walk to units within a hero's army, similar to the items that grant Umbral Malady Immunity introduced in Eldritch Realms. Similar infusions should likely exist for desert, arctic and desolate biomes, and be unlocked automatically by the associated race trait (or Primal subculture). However, this is particularly important for the underground because it doesn't have the surface's abundance of roads.
Ultimately the bigger contribution from my Underground Adaptation trait was to allow me to settle the desolate biome immediately above my capital. Lava chasms and pools are more numerous than they used to be, and I don't think it was simply a consequence of playing on the Crimson Caldera map. However I could have also gained this benefit with the new Desolate Adaptation trait which might have netted me a better early game.
Speaking of lava, I found that the pickups in small pools (two tiles) could be hard to see if they weren't simply invisible because of height variations.
Item forge
The item forge changes are working as intended. I did forge a tier 3 weapon in order to ugprade my ruler early rather than waiting to make a tier 4. I also tried to fill my heroes' slots with affordable T2 items. However, this did highlight the weakness of the item forge system and its associated randomly generated items: It's a lot of clicking to ultimately eke out +1 defense here, +10% accuracy there. When you only checked in the item forge every 4 turns to make a big purchase, it was fine; not so when the system churns out items so fast that the item forge ends up idle for lack for work. I've not been fond of random item generation since it was introduced and this experience has done nothing to correct that.
Balance is a greater concern with the new looting mechanic when heroes are defeated: A wand of Summon Spider Monarch fell through my fingers as the game felt a crown with +1 defense and +2 status resistance was worth more. They were both tier 2, inexplicably.
Faction colours
The ogre update adds a bunch of faction colours to the game. It also changes some of the existing ones. I'm not fond of the darker, bluer pink it's introduced. I think it doesn't work well in a number of allowed combinations as a foreground colour. I'm also a little surprised at the inclusion of five different browns, some of which are called orange or yellow.
While many primary colours were added, the selection for the secondary or foreground colour remains lacking. In particular, there is still no option for a bright red foreground colour. I won't bother you with the rest of my preferences, but that colour is one I've seen requested repeatedly and I have to assume including it only as a primary or background colour is an oversight.