One thing that would help is randomly generated quests. Any person in the game will ask you to do something for them, a bit like random encounters with a bit more fun.
Maybe allowing you to improve you companions skill/perks, etc would be good.
Why play a story based rpg, If all you want is more stuff to colect. and more levels to gain, in a completely random ( which it never will be given finite locations and stuff to collect, creatures to kill ) generated manner.
Oblivion yes you can play on after the main quest having done so many times, and you can do almost everything without even touching the MQ. But after a bit it gets hollow, go to cave use the same techniques to clear cave repeat. collect armour see its one you already have repeat. Buy house fill house with junk repeat. Talk to the whole town find nothing new repeat.
After a few hundred hours wnen you have explored everything, and you are left with no story hooks just leveling all your skills to 100. You are not playing an rpg just a number game with pretty pictures with at best a throw out comment such as "hail saviour of our nation" from npc's you saved ( even though their township is wrecked, they go about doing nothing ).
So just stretch yourself start fresh and try something different, not just getting to the top and admiring how tough your character is with all the goodies he has.