It was banned in Standard barely a month after is was released
It provides the ability to grind out when you run out of cards, almost giving you an extra card draw each turn, but better, as it's a permanent of your choice from your graveyard, nulling any efforts by your opponent when using removal spells
The number and range of alternate-art and alternate-frame printings exploded compared to previous years, offering an official alternative to popular but expensive fan-alters
Its a lovely, well-balanced deck
The amount of Vault Progress Points depends on the rarity of the received card
Because you cast whatever creatures Azula swipes, you don't need to worry about giving it back if your opponent removes Azula like you would with Mind Control variants, and the enters ability means your opponents are always two-for-one'd at best