I guess that knowing in advance that the main game ends has been an advantage to me that I know I have to get as much done as I can before finishing the main quest, becuase of this I've spread out doing bits of the main quest in between all the side quest and random exploring stuff.
When I think about it though this is exactly what I did with Oblivion, I didn't feel like I wanted to get through the main quest then carry on with the other stuff, I felt like finishing the last mission was my goal and that the journey to get there would be more enjoyable if I spread it out.
What has also helped drag out the main quest is not really having a fixed goal at any time, several times when on my way to a main quest location I've become distracted with other quests or locations to explore. Another reason is coming across something I'm not at a high enough level to do, like a computer I can't hack (One example being a locked room in Vault 112
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