If you look at all the new skills for the new classes, the barb one looks the least exciting. The idea and the reasoning behind it is good tho. I think they should improve the animation. The falling rocks don't really seem to have a real impact and they seem surreal bc they dissappear immediately on impact. They should take the time to apply physics to them, make them roll on the ground for a bit and break sometimes. And there should be ALOT more rocks.
The Monks new skill looks like a really good skill. It's a 2 minute cooldown which is extreme, but with Cooldown reduction coming from gear, legendaries, gems and Paragon points, I think it should always be available when you need it.
The Barbarian's avalanche doesn't really have a place in my opinion. It's just another AOE damage attack that matches Earthquake, SS or Hammer. Perhaps there will be some unique runes for it.