It's weakness is it can be destroyed without any permanent-affecting cards. You can save your steals/deflags for important cards like weapons and graveyards.
Worst case scenario- it's a speedbump. Just keep playing your deck like you would normally and it will fall. No strategy changes are needed to deal with it 95% of the time.
Uh-huh. You say that if you have FFQ or Boneyard and good creature control, and they don't have a Rain of Fire to wipe all that. If you have a small, fast deck with a few dragons for damage, or something with Growth/Ablaze? Yeah, right, that Bone Wall will hold forever. Doesn't matter if you keep four 51/51 forest spirits alive if they can kill two of their own fireflies or skeletons each turn. But hey, mass weenies doesn't always work either since they just stall with other means until they can play a Bone Wall and Rain of Fire on the same turn and suddenly have 40 shields.
Both Bone Wall and Rain of Fire cost quite a bit, and forty shields isn't that big of a deal if you're a mass creature deck.
But the point is no card should have only one counter. As it stands now, if you don't have a mass creature deck, if you face a bone wall, you will at best have a difficult time, and at the worst you are screwed. And face it, not everyone is going to want to play a mass creature deck.
I also do not agree with the contential that 'all' you have do do is save your deflags/steals and play them at once. I am all right with one card having the potential to tie up a few cards, but if you have to play 5+ cards just to deal with one, the card is not balanced. Because once you've played your deflags/steals your opponent can just play another one (and another, and another), and where are you then?
My suggestion is to implement one or more of the following:
1. Steal/Destruction type cards eliminate 3 Counters.
2. Bone Wall only gets counters from the destruction of opponent's creatures.
3. Bone Wall only gets one counter per creature kill.
Even if all of the above gets implemented (and I am not necessarily advocating
all of them together, I think 1 plus either of 2 or 3 would do nicely), Bone Wall still remains quite potent and still keeps the potential of stonewalling the opponent, but it decreases the likelyhood that it alone will stop your opponent cold for the entire game.