I'm not going to try to argue you out of your opinion, and I don't begrudge the fact that you didn't like it. Just thought I'd start off with that.
I don't think disappointed readers were taking issue with the dark or tragic tone
I'd not try and put everyone in the same box. I definetly see a lot of people who did take issue with the fact that it didn't have a happier ending, which I find extremely surprising for the same reason you metioned - they made it this far, what did they expect?
Speaking for myself, it feels like I was waiting for a payoff that never came.
This is what most people say, but there are plenty of "because reason X". Plenty of people disappointed and each of them a different reason
The story abruptly ending with the No-God's resumption wasn't satisfying to me, it was expected and derivative of what I've already seen in Akka's dreams. For the Mangeacca to be long gone, the Consult leadership already subjugated, and just more Sranc, Bashrag and Wracu at Golgotterath, it was too much stuff I had already read before and none of the surprises I had been anticipating. I really didn't like that we saw more of the Ark in the Thousandfold Thought than we did in the entry titled "The Unholy Consult."
That certainly does seem to be what happened.
I do think it would have been odd for a bunch of new monsters to have been introduced right at the end, for the same reason that the Dunyain being in control seemed strange - there was little foreshadowing.
This isn't about subverting the audience's expectations, which I know is something Bakker set out to do.
Just to clarify "this isn't about" refers to your dislike of the ending, not the subverting expectation itself.
While the quality of writing is much higher in The Aspect Emperor, the story structure and pacing does not live up to what he accomplished with The Prince of Nothing. Every novel had an insane stand-alone story. Every main character was a completely different person at the end of each book from who they were when they started. Every chapter is momentous for the overarching plot. Assumptions you had beforehand were completely blown away. These books instead felt like they had a lot of filler and were clearly incomplete fragments of a single narrative. The Unholy Consult really had to make up for that dissatisfaction with a solid and original resolution it couldn't afford to end in essentially the same fashion the preceding novels did. Instead, saw more of the same and there are plenty of plot threads left dangling.
I didn't see that big of a difference between PoN and TAE, plot wise. They are actually very well mirrored, imo, and TTT/TUC end very similarly.
Though, for the time spent on each (ignoring the "20+ years" spent on TDTCB), I think the pacing of TAE wasn't as masterful, which is strange given how much time he spent on it. I honestly think he just spent too much time writing, editing, and rewriting, to the point that the story did suffer.
FWIW, though I do see now that it was wishful thinking, I was hoping for a lot more 'answers'. I thought there'd be a lot more world-building, rather than new mysteries. I had similar complaints with Malazan's final book Crippled God. At some point it is a story, and it does need to end, and the reader is no longer interested in new mysteries - they want the story completed.
Yes, there is another series after TAE, but to be hoping for answers is probably unwise. TTT ended like TUC, and to think that TNG will end otherwise is folly. These are the books Bakker is writing.
