Why are some open worlds addicting to explore while others feel like a chore?

Players will happily spend 100+ hours exploring the world in games like Skyrim, Fallout, or Elden Ring, but in other games, players complain that it feels like a chore and they quit before 20 hours. The games these players are quitting - they have cutting edge graphics, smarter enemy AI, and even a variety of activities for players to complete, yet players still don't care and inexplicably they boot up Skyrim again... Why is this happening?

The answer lies in one of the most powerful tools in a game designer's toolkit: random reward schedule psychology. You're almost certainly familiar with it. The basic idea is that intelligent beings will be motivated longest by rewards that are given out at random intervals. It's the driving theory behind gambling, lootboxes, Pokemon cards, etc. So why aren't level designers thinking about this when building open world POIs? Some may even argue that they are doing this "we give random loot at POIs" or "we have semi-randomly distributed activities across an area."

In an average open world game, you have a variety of activities for players to do, and most them are pretty fun.

In iconic open world games, there are still a variety of activities, but some of them shatter player expectations. Players will happily accept a few bear caves if there's a promise of unique & incredible POIs in the future, but if all POIs are formulaic, players will grown bored of them, even if they are all well executed. If all your POIS are 7/10 experiences, players will remember your game as a 7/10. If some of POIs are 4/10s, but others are 11/10s, players are going to remember those 11s much more strongly (for more on this, watch the first 11 minutes of this video: https://gdcvault.com/play/1035410/Tencent-Games-Developer-Summit-Noise)

POIs like Elden Ring's Siofra River and Skyrim's Blackreach change the possibility space. After discovering these places, when players find a POI, they don't know whether it's a small cave or another world. Because these spaces are so cool, players are compelled to explore to make sure they are not missing out on another incredible secret. Exploration becomes addictive.

https://www.youtube.com/watch?v=SZEaXRrXNx4&t=3142s

Joel Burgess & Nathan Purkeypile actually snuck Blackreach into Skyrim. It was out of production scope, but they were passionate about it and found time to sneak it in, and it's one of the most iconic locations in the game! This shows the immense importance of ambitious level designers and how creating close relationships between level designers and artists can yield incredible results. Also, this is generally one of my favorite videos on level design. Notice how there's not a lot of discussion of geometry or wayfinding. These are the fundamental tools of level design, but great level designers are also storytellers, artists, and game designers.