I think Minecraft gets it right by using procedural generation to add depth to the existing content rather than making different content.

There's a fixed set of biomes and notable geographical features designed by the devs, so there's no incentive to keep finding unseen ones, but each world gets its own layout and landmarks, so you get to explore the details of that specific generation for days without carrying over your knowledge of the previous one.

In the long term it might get repetitive too, but it does at the same rate as one gets tired of any other game I think.