As far as the bending failure thing, I dunno... I do and don't like the idea of it. I like it because when you're doing precise martial arts maneuvers, well, anyone who's ever done martial arts to a moderate degree will tell you that you need to be unencumbered or you're not going to be doing it well. Maybe all benders (save Airbenders) can wear light armor without penalty, but then they incur normal ACP when bending in heavier armors. Then they could take the Armored Bender feats I proposed to wear the heavier armors (provided they're proficient in them).
I also support the Immobilization rules.
I like the new Ice Spikes, getting a cool imagine of a Waterbender who fights with a frozen greatsword, wearing ice armor, and generally causing havoc in battle. Also helps the unbalancing angle of the 7d4 ice blast at level 1. Good good.