Skyrim is the sort of game you can complete a questline then go and play something else and then come back to. I'm currently playing through the Dragonborn add-on with my original character. I tried a couple of the player made add-ons Wrymstooth and Moonpath to Elsweyr which added around 10 hours.
I still haven't done everything in Oblivion and I bought that when it came out.
