Wow, I've heard of top-down sets, but this time the top is down.

I'm a little dissapointed that the lair land subtype didn't make a comeback here, what with all the lands that depict the lairs of various creatures.

Deck of Many Things is even more swingy in D&D so that checks out.
I think it is fine. In any format with steaks I don't think it is strong enough to matter. There are plenty of other lucky draws that can lead to winning on turn 6. At least in limited it looks like there is a fair amount of maindeckable artifact removal to keep your opponent from getting too many rolls.

It actually bugs me that Deck of Many Things doesn't have much worse outcomes for its controller on bad roles. That artifact is known as a campaign-killer because it's HUGE risk, HUGE reward, and minimal effort.

Sphere of Annihilation is also kind of a fail as a top-down. The Sphere typically sticks around, with its core traits being deleting anything it touches and people (especially casters) being able to struggle for control of its motion. An artifact with an ability like "Discard a card: Exile another target permanent. Any player may activate this ability but only when they could cast a sorcery" would evoke its abilities much better than a time-delayed wrath.