This could actually be really sick. PLay this on turn 4, and your opponent has to remove it or you will get a huge tempo boost.
4-mana 3/6 is premium stats, not many decks can deal with that much health easily on turn 4. Fandral saw play in early Old GOds and was played as just a 3/5 that people had to remove. This is a similar effect.
Then again, we'Ve seen time and time again, that good HUnter legendaries aren't enough most of the time.