I played BOTW first and then TOTK. The world is the same (without underworld and sky), but there are changes off course. Still lot of places, characters and enemies are the same. There will be stuff you will be missing in BOTW (building mechanic in example or custom teleport places, or weapons break faster because you cannot attach anything to it). So it doesn't feel like a complete new game, as TOTK "feels" like a DLC (admittedly its more than that). After lot of playtime in TOTK I went back to the previous game recently to complete more of the tasks. And its is super confusing which parts of the maps I already visited; thank god I can enable the footsteps in the map to see where I was already.

Sooo, is it worth playing the predecessor? I say yes, if you really like the world and did most stuff in TOTK, but want more of it. It has ton of shrines and I loved the big dungeons as well. And it has some interesting DLCs I still have to do. But in some ways it feels like a step down, because of the skill sets. But it has some tricks on its own on the sleeves. If you are okay with playing in the same world, want more of the game, then maybe yes if you can get it for cheap. I wouldn't call it a must have in my books.