I agree with it being balanced for the most part. However, I think that creatures that had damage prevented by an ice shield, (1 str blocked by ice shield,) should still have a chance to freezing. It makes no sense to me that they tried to attack, the shield engaged and prevented it, but there is no chance they will get frozen. If the touched the shield, they should have a chance of freeze. 0 str creatures should be the only ones that don't attack at all in my opinion.
This is pretty minor though, and I don't use an ice shield in any decks, so I can't say I care all that much either way.