I played Skyrim on a older platform. When I got the newer platform, I got a new copy of the game. Since my saved game was on the old platform, and it wouldn't transfer, I had to start over.
This game is the opposite of linear. In fact, I did the main story line only until I could branch out and start all the side quests. I notice there are definitely differences between my characters and the things I am doing between the two games.
Some differences are a conscious choice, like playing a different race, or choosing to not do a particular quest because I don't want to end up where it goes. Some just happen, like different houses owned, different cities visited, etc.
If the game is enjoyable enough, or open enough to keep things interesting, replay can be a fun and rewarding experience.
Don't get me started on replaying Skyrim, or Elder Scrolls games in general.
Though, one thing that I have noticed is that they're very different from replaying other games; at least with more modern Bethesda I tend to replay them with different mods for different purposes (for instance, playing Fallout 4 as an action-horror game).
One of the things that I think goes on in Skyrim and a lot of those other games is that the actual core gameplay loop is relatively light, and it's the breadth of content rather than mechanical depth that carries the game forward.
I haven't actually finished an Elder Scrolls game. I play a bit of the main quest then I park it in the garage and never go back. There is so much else to do that I stay busy that way. Maybe I should try completing Skyrim sometime just to see how it goes.