It was the Underworld Ascendant of it's time. A rush job thrown together because they ran out of time, money and ideas. It was fucking dreadful as a stand alone game, let alone as a conclusion to a story begun with U7.
While Ultima 9 was terrible, it still was a fully functional game. The Underworld Ascendant of it's time was more
Descent to Undermountain or other barely functional "games"
I'd agree that U9 was nowhere near as bad or broken as UA, but I don't think functional is really the right word to describe it. U9 had some horrendous bugs - some of which actually broke the game. I remember that, when I was playing it at release, a teleporter in a dungeon near Minoc basically just crashed the game and broke my save file. So that is as far as I ever got in that game.
However, the big difference between UA and U9 was, that Origin knew how to pull off an asset-based exit strategy - that means, you take everything you made (scripts, 3D objects, sounds, textures, etc) and you somehow punch it together into a game that works just well enough so it can be sold. That's also why the dungeon of Hythloth is based on assets of the (originally planned) Britain sewer system.
UA, while also trying to pull off the same trick, couldn't even get that right. I can't really tell what on earth they were thinking and my memory of the release version is slowly fading away like a bad dream.
Maybe it was this: U9 had competent programmers, with too little time (to finish the last version of the game) and bad direction, while UA had incompetent programmers, with too much time and bad direction.
I do have to say though: Today I like U9 just for the fact of how much of a mess that project was. It's outright interesting to dig through it and come up with reasons why they did things in a certain way.
Also, quickly putting together a game brought about some hilarious results like the pirate of Austin, Texas. You can somehow reason over it (like the pirate somehow fell out of the moongate like the gazer) but it's just so silly.