I would suppose in a deck with this shield, you would also consider including heavy creature control. Likewise, I have created my own Weight/Petrify deck to have essentially the same effect (make everything too big for the shield, which then permanently blocks damage.
However, there are plenty of strategies that basically ignore this shield.
1) Spamming units is a proven strategy, and rarely are those immaterial.
2) Momentum, a basic for any deck that hates shields.
3) Destroy/Steal. While you could enchant the shield, this is also true of other permanents that could be deemed "overpowered" when enchanted (Fahrenheit, Eternity, Pulverizer, etc).
4) Quanta control would work for limiting a player's ability to immortalize or antimatter your units.
So yes, this shield would be very powerful against some decks, but very worthless against others. This is similar to many alternatives, such as Fire Buckler, Diamond Shield, Jade Shield, Hope, Gravity Shield, Bone Wall, and Permafrost Shield.
In fact, I believe many people would still choose Bone Wall in their CC decks, because it can reliably prevent all damage per attack, rather than being dependant on the creature to be immaterial.
As a final note, I would suppose that Zanzarino, because of the way he has handled the game so far, would not introduce a card such as this without also including a card capable of defeating it -- such as the ability to remove immaterial status from your own creatures. He tends to balance things that way.
Thanks for the comment.
