Personally i don't have a problem with the blood imps, i hate the card and the fact it exists, but its not broken.
My issue with these zerg decks is that because of warlocks' life tap, these decks are beyond the point of just being "good". this game revolves around card advantages more then hp,
Cards > HP in almost all cases.
Its hands down the strongest hero ability in the game, Mage is annoying as hell sure, but 2 cards a turn is pretty much gg against a deck that has to spend the first 5 turns on the ropes, play its aoe and wipe the board..then because of life-tap, the card supply is still there to play everything over again.
Blood Imp is fine, I think Life Tap needs a look, card advantage is much more important then hp.