Jin-Gitaxias, Core Augur forces your opponents to discard down at the end of their turn, while you draw into dominance
Artifacts are historically the most powerful card type in the game, and almost every time there has been an artifact-focused set it has caused something to get banned one way or another (Tolarian Academy, Memory Jar, Seat of the Synod, Skullclamp, Mox Opal, etc)
Currently, a near mint example from this set will run you $300, while copies from Limited Edition Beta are only $125
We're looking at Colorless cards, with a focus on kitchen table formats like Commander, Five Color, multiplayer, Highlander and Peasant/Pauper
This is the biggest reason to favour Reunion over Discovery Lifegain attached to Thrilling Discovery: Its a minor addition and it helps you negate the life loss from our manabase