Personally, I'd like to see how well it works with a fighter type. Mage-types spend most of the time waving their hands about, casting spells, so the reaching and grabbing motions would be intuitive. Would a fighter character actually make swinging motions?
No, you'd be making the same motions. The motions aren't imitating the actions; they're activating programmed responses assigned to keys. "Reach right" doesn't correspond to "some spell," it corresponds to "3," which is the key you assigned to Frostbolt or Heroic Strike or whatever.
Some classes would be a bit slower than others, though. Ret paladin? Actions every few seconds as things come off cooldown, sure. But a Rogue? It'd look like you're playing DDR with the amount of flailing around you'd have to do to keep up with all their actions in combat. Leaning forward/backward for movement also seems pretty sketchy; you'd have to have perfect posture to not move around all the time, ne? Camera control also looks kinda chunky. I dunno, there's potential, but it'd need some serious smoothing out to even be considered practical at all, much less competitive with a keyboard/mouse combo.