I suppose the grin without a tooth could represent the image of a mischievous child (that image of a little kid missing a baby tooth, always up to no good that we often see on cartoons)... Personally, I would like him to have all his teeth, but the face and the hair are what I like less about the redesign. I love anime, so I'm all for spiky hair, but I don't think it quite works on Loki. It would look better messy in my opinion, not all up in the hair like he touched something with static electricity.
Lee Garbett sent me another answer in private (so I can't sent you guys a link, but I swear I'm not lying), and he said this about the original concept:
"Looking at it fresh, I can see a lot going for the original. His hair is probably better. "
As for New Loki's power, absolute power corrupts absolutely, so he needs to have limitations to what he can do, or else he'd be too much overpowered.
One thing I've been wondering about is that now King Loki thinks young Loki is dead, and he'll go back to Asgard and face Freyja. So, he's probably going to to tell her that young Loki blew himself up. I really, really want to see her reaction and I hope she shows sadness or even anger, some sort of emotion for her adopted child. That might start to redeem her in my eyes. I also wonder how the other Asgardians are going to react.