Pretty good nerf. It's as if this really only affects face/ aggro style decks. I use this as more of a tech card in midrange/ control decks so an additional mana for that powerful of an effect plus additional board presence yeahhhhh I'll call it fair
Fine nerf in my opinion, Ironbeak Owl and Keeper of the Grove were the most prevalent silence in the game, so by nerfing both of them they encourage people to play the more costly Spellbreaker, but silence on turn four instead of turn 2 without tempo loss, or at turn ten silence + 6 mana left is a lot different from silence + 8 drop.
Now shaman will play Earth Shock a lot more, and priest may even play Silence, and if you 're not playing one of these 2, you'll pay 4 mana or take a tempo loss for your silence.
Very bad nerf :/ Should have been 2 mana 1/1. That would prevent it counter 2 drops and still make it a tech choice that is needed in the early game or playable later with other cards. Now if you want a silence Spellbreaker is the auto include.