I'm not sure if any game before WAR has ever featured knockbacks, but for me it's a brand new mechanic.
For those of you who haven't played the game or seen knockbacks, they are simply attacks that cause your target to go flyyyyying back quite a good distance over the battlefield. They go up in the air quite a nice way. Knockbacks are full of win because:
1) They are extremely fun to use. I lol every time I use one, usually making the weeeeee sounds as the other person flies through the air.
2) They are actually kind of fun to have them used on you! It's such a funny thing to all of a sudden be flying through the air, you can't help but laugh a bit. Of all the debuffs I've ever seen in an RPG, I actually don't mind being the victim of this, and that's an amazing thing.
3) They have great strategical use. Knocking people off cliffs won't hurt them (you take no damage from the fall when knocked back), but it can still put them at a serious positional disadvantage as they run back to scale the cliff. You can knock melee DPS away from your backline. You can knock enemy backline INTO your melee DPS. You can knock enemy healers away from the fray, allowing your team to score an easy kill on someone else. Etc.
4) It's a debuff that allows the person it's used upon to change their tactics a little to diminish the hurt. For example, you're a melee character pushing the enemy backline, when suddenly you're knocked away.... you land close to your own backline, giving you a nice opportunity to lineback some melee that are hurting your healers there. Or, you're knocked far enough away from the fray to make a retreat if you were looking for an opening to. Or you run off to capture another shrine instead of the one you were heading towards. Etc.
There are so many cool situations I've seen from limited use of this skill already.
Yesterday I was approaching a PQ area that takes place at the base of a cliff, which I was going to carefully scale to join in. When all of a sudden I stumbled across a shaman! I leaped to the fray and tried my best to take him down, but couldn't put him below half health. Except, he was standing kind of close to the edge of a cliff -> position myself -> *thwack* shaman goes flying down. Shaman lands in the middle of several enemies, who proceed to make mincemeat out of him, to my immense satisfaction (and maniacal cackling).
In Mourkain temple (tier 2 scenario) you want to try and take down the guy who's captured the relic thingy - he has a big glowing red column above his head. Often he's tough to kill because he's hiding in the backline. A couple of time I ran in there, got behind the lucky fellow, turned around and *thwack* knocked him out of the park (into my waiting team, who slaughtered him).
I heart knockbacks.