But there's just something fundamentally replayable about Skyrim. Dropping in new items and questlines is fun.
Removing the intro quests and starting a new character in a truly open world is fun. But every time I fire up Skyrim again (or if Todd Howard decides to port it to something else and take my money AGAIN) I always find something new to do. I've played certain MMOs for 16-plus years, but generally speaking regular offline games have a lifespan for me. Skyrim will turn 10 this year (still 10 months from now to be fair, but this year) and I still keep coming back to it, which I really don't do with single-player games. All the stuff I've done a million times, but yet again finding a way to do it differently. I'm leveling conjuration, which is a school I never tried.
The only rule I set for myself is 'Don't be a stealth archer. I recently decided to install Skyrim again and after installing every mod that looked cool enough to try out, I found myself fully sucked in again.