People are overreacting to this card. This card is exactly what mutate should have been to begin with, instead of how stupid it is now.
You get the same mana benefit as Mutate, spend 2 mana, get a 3 cost boost rather than spending 0 mana to get a 1 cost boost. But this SEVERELY limits the combo potential of this card, in addition to limiting how early you're able to play it for the first time. Almost every broken mutate interaction is playing something and then mutating it immediately on the same turn (usually after using your rush minion to trade favorably). A turn 3 or 4 Mogu Fleshshaper was very common, which meant an 8 drop very early in the game, when it was often impossible to answer.
This card costing mana means it's far more difficult to evolve something in the same turn, which means you may have to get the minion to stick a turn before you can evolve it, and then have to wait another turn after that to attack with it. If it sticks, there's a higher payoff, but it gives the opponent a much greater chance of being able to answer your minion before you can evolve it, or because the evolve is likely to happen later in the game, have access to larger suites of removal to deal with the larger resulting creature.
The mechanics is to evolve is fun to play but it is not fun when you agaist this type of deck. Remember the halloween event that brought evolution back for a limited time with the rabbits. Another meta full of shamans with Mutate, Explosive Evolution and Zentimo is approaching. Nerf will fall.
WHY does Blizzard insist on pushing this mutate crap? The majority of the playerbase hate playing against it and it's also frustrating because Shaman seems to have been pushed into being RNG based. Sigh.
The whole purpose of Hearthstone is o be an RNG fiesta machine. It's not just shaman that's pushed in that direction, mage is also going the same way. Look at their new hero card or their quest card.