In the old days of hearthstone Dr. Boom reigned supreme in the 7 slot. He dropped 9/9 worth of stats onto the board and his boom bots would randomly blow up enemies for 1-4 damage when they died, so he combined a massive pile of stats with extra effect. Dr. 7 saw play in every kind of deck because he was a great finisher for an aggressive deck and a great stabilizer for a controlling deck. In fact this was one of the real problems with Boom - everyone wanted to play him.
A neutral card with immense value and which was good in all kinds of decks - many people saw the good doctor as a real problem. Fast foward to 2017, and there is a new doctor in town, with many similar issues.
Bonemare is a neutral 7 drop that puts 9/9 worth of stats on the board. Those stats also have extra goodness because 4/4 of those stats can attack right away. Very similar to Dr. Boom in many ways. The thing that makes Bonemare just not as good as Dr. Boom is that it requires a minion in play to work. That isn't a big ask, but it is something. Dr. Boom can be slammed down in almost any situation and be good while Bonemare can be a weak draw if there is a clear boardstate. Pretty much the only time you draw Dr. Boom and sigh is when you are going to be killed before your next turn.
I got a couple of Bonemares in a draft deck I was playing and it was an absurdity. If I got to turn 7 with anything in play I just won by slamming Bonemare after Bonemare. In talking to people about it there was a clear sentiment that Bonemare is a problem. I think Bonemare's problem is different than Boom's, though, simply because of rarity.
In Constructed play both cards saw a lot of use, but Bonemare wasn't unfair, just really good. It is actually a good thing to my mind to have a common that is a powerful late game card. Beginners often feel shoehorned into aggressive decks because they simply don't have access to the expensive legendary minions required for a late game and Bonemare gives them an out. Bonemare is common and provides a thing for people with limited collections to do in the late game, and I like that.
When drafting Arena decks though Bonemare is a disaster. Dr. Boom was absurd in Arena but at least you hardly ever saw him so it wasn't such an issue. Having Bonemare in the common slot often means that you may have to face down multiples of them and there is often nothing you can do to play around that raw power. They just make too much stuff too efficiently and leave no realistic counterplay. When you have a deck with normal late game cards in it and you go up against one that has multiple Bonemares you simply have to win by turn 6 or accept that you are getting blown out. I am not a fan of that as a common thing, and right now it is a common thing.
Well, up until this week it was a common thing. Now that the new Kobolds and Catacombs expansion is out the extra appearance bonus for Bonemare is gone and it should go back to being something you see on occasion instead of something you see constantly. That is better for Arena, certainly, as Bonemare is just too far above the power curve. However, Bonemare is going to continue to let people with few resources have a power play in the late game in Constructed, which is a thing I like.
Overall I think Bonemare will be a positive contribution to the game. It mucked up Arena drafting a lot for 4 months but it will be in Standard Constructed for 16 months and I like what it has done for deck building. It surprised me honestly to see just how powerful Bonemare was, and I think it surprised a lot of other people too. Now we know - 9/9 for 7 mana with extras is superb. I should write that down somewhere.