That card just completely kills Control decks. Turn 1 creature, Turn 2 creature. Cast this on your Turn 3. If they sacrifice lands, they lose the game because Control cannot afford to do this on Turn 3. If they don't, your guys gain both +5/+0 and Control basically loses too. This is way way too good. Balancing Act is a really fixed Balance.
Is it a bad thing that it kills control decks? Plenty of cards kill control decks. There's no rule that says aggro decks shouldn't have bomby cards vs. control decks. This does nothing against an aggressive creature deck, and even against aggro control might not do anything. Combine with the fact that even control has turn 2 answers (mana leak/condescend and family or even creature removal) mean that this isn't gamebreaking. I'm not sure that this would be considered anything other than a decent rare that johnny, timmy, and spike all appreciate for different aspects. Hell, this could be a potentially good finisher in control, too.