The obsidian rune looks really nice to me. If the higher runes increase it's duration it'll be a nice setup to pop that up early and switch to other AoE attacks or start sniping people off with single target strikes.
I love the obsidian version of it... and just imagine having that persistent aoe combined with cc and movement abilites... first hit dashing strike + second hit crippling wave + third hit obsidian sweeping wind = sudden, inescapable, swirling wall of death in your face...
It does make me wonder though, will runes only effect the the third strike for combo skills? Some of them I can see working on all attacks (the fire damage and spirit generation for instance) but otherwise it looked like only the finally attack was modified in anyway, other then visual effect of course.
Most of the combo skills we were able to use in the last 2 blizzcon demos did something, plus their damage, at level 1 and 2, with the bigger effect at level 3. (IIRC the exception was exploding palm, which did nothing but damage until the final effect.)
So it might just be that Sweeping Wind here doesn't deal any effect other than dmg until the final level, and the rune effects are just continuing that. Where as a combo skill that did add some effects (buffs or debuffs) with each level up would have those emphasized by the rune effects as well.
Or it might be that we can't see it since there are not enemies there. Maybe level 1 hits 2 enemies, level 2 hits 4 enemies and stuns, and level 3 hits up to 10, etc. We can't tell without the full skill tool tip to read.