I felt that very same thing in act 3. I know that the paradox of urgent main quest and and lots of side quests is a common thing in these types of games, but I truly think that the sheer VOLUME of stuff in the city brings that problem to a new level in act 3. It honestly feels like the game should have finished in act 2, and act 3 could have been its own game, with the amount of STUFF it brings in and has us deal with. A whole bunch of new plotlines, stuff not related to the main story, stuff that IS related, there's just so much that it's easy to just become numb to it all.