It's unfair in its ability to slow down other game plans without affecting your own
If youre using Vadrok to cast it, this functions the same as a Wheel of Fortune would
This means, for example, that a Modular creature would come into play without it's +1/+1 counters and then be destroyed by state based effects
Any creature you control that couldn't be targeted by the original spell (due to shroud, protection abilities, targeting restrictions, or any other reason) is just ignored by Zada's ability
I think fans are going to want that Beseech the Queen card quite a lot
As long as neither player is manipulating their library or using their graveyard, using a Millstone does nothing but reveal information until the player being milled runs out of cards, but it took more explanation than you can possibly imagine to make players understand this