There are some things with World of Light that are pretty interesting, but I don't find the spirit battles to be one of them. There isn't really any difference between spirit battles in WoL and the ones on the Spirit Board, so it's just like a copy/paste for two 'different' modes. Subspace's trophy acquisition was drastically different than the game modes like coin launcher that were designated for getting trophies outside of adventure. So World of Light's appeal for me is more about the big picture of progression than the battles themselves, which I feel kind of bad about. The spirit battles themselves are fine, but they still really are just overglorified event matches more than anything, and the Spirit Board feels like a better representation of the event match style, and the adventure mode should have been more adventure-esque. The map interaction is more immersive than the battles are, and is probably its greatest appeal. The boss fights are well done too and I really love Galeems fight and
the actual boss fight is literally a meme come true about my light jokes comparing him to a certain light themed boss from Hollow Knight , but most of the bosses in WoL are also in classic mode so it sort of goes back to it having less uniqueness than it could. Subspace's bosses were exclusive to Subspace until you unlocked the boss rush mode (which Ultimate sadly lacks as a designated mode as well), and having already fought a lot of bosses in advance, I didn't really find much surprise in who I had to face in WoL or discovery in how to fight them. There are some really special moments in WoL but it's a pretty long grind to get there.
Since revisiting WoL last night, I'm not as negative about it and have had almost a year to let my view of it ferment... but I still feel it could have been a lot better. More than anything, I want a prequel to it, show the characters teamig up and learning about the threat of Galeem. As far as what World of Light is, it's essentially a very dragged out version of the endgame Subspace levels where you had to reawaken all the fighters after they got turned into trophies by Tabuu. Again, the before would have been nice to have.