When you're far enough along, this game becomes more about waiting for the 24 hours to be up to dismiss an impossible to complete objective. When I don't have 30 dwellers to max out charisma on, and I certainly don't have the desire to kill off dwellers I've worked hard on, it gets frustrating to wait out the 24 hours, just to have "raise charisma of 30 dwellers" replaced with "raise the SPECIAL of 28 dwellers".
Furthermore, with the carry-limit on dwellers, it's getting tough to keep dwllers our long enough to meet the hours in wasteland ojbective.
Finally, of the objectives I can acheive, they are all just impossibly long. I'm up to selling 1162 items, and I have a storage capacity of 250, this takes ages to complete. When I've got that, along with extinguishing 42 vault fires, and "raise the SPECIAL..." that I'm waiting to get removed, it just takes all excitement out of the game.
The larger caps rewards don't really make up for it either. I've long since maxed out on caps, and there's nothing at all to spend them on. I'd rather have smaller rewards and objectives that take less than three days (or more) to complete.