Breath of the Wild is a great game, but the fun comes from the gameplay itself. It's a giant sandbox full of systems that integrate well together in a way that hasn't been done in any other open-world game.
But it's also a game that doesn't reward you in any way that changes the gameplay meaningfully. It's the same from beginning to end. The combat is the same, the weapons break constantly, and there are just a few enemy types.
Elden Ring doesn't have those well-integrated systems but is chock full of activities that reward your exploration and getting good. There is simply nothing like it out there.
It also puts what made Dark Souls great in an open world, without taking anything away from it. BotW is LoZ without dungeons and real progress. Don't get me wrong, it's still a fantastic game, but I consider Elden Ring the best game among the two.