I think making the city a hub would be a good design decision. You're constantly going out to other areas to explore other things, but you come back periodically and see more of the city and experience more quests. I think the big problem is that the scope of the city makes the structure of the game just fall apart. Act 2 feels like a major climactic moment, moreso than the end of act one. After that point everything just shifts massively. Then you start act 3 in a small town, dealing with its problems, it feels like you're at the start of an entirely new game when really things should all be coming together. You're essentially presented with a whole new slate of antagonists. The cult of the absolute that's been your main foe for two acts is revealed as a puppet for new bad guys that you're only just introduced to, who have their own forces that have barely been hinted at. The story throws so much new stuff at you at the same time it becomes more dense with content than ever, and it just turns into a mess of sidequests.
