Slivers can seem unbeatable, especially in casual Commander
Just by attacking, you sacrifice another creature or artifact and deal damage equal to its 2 plus its mana value, an effect that usually counts the sacrificed creatures power
There may still be advantages to having a creature start face down so you can later turn it face up
The key distinction between the mythic lands and the others is that the land side CAN enter the battlefield tapped
As this is a special set, there will be no Booster Boxes
So as a whole, I would say its obviously very good for Japan, but more than anything, its just trying to lean into the authenticity of what it represents to that market what the history is with respect to video gaming culture in that region, and making our players globally excited.