Current State of Balance
First of all, the game is probably the most balanced its been since the cinderhulk meta. There are very few champions that are just overpowered to the point where they are a must ban every single game, except for graves. The champion variety in mid, top, support, and adc is pretty good, but the variety in jungle is severely lacking. There are very few tanks played in the jungle currently, besides the occasional gragas, zac, and ww.
I don't think that snowballing is as bad an issue as it has been in previous seasons. Masteries are a tad better now, although I think some work needs to be done on grasp of the undying.
Overall I am pleased with the current state of balance, but do think the jungle needs to be looked at in more ways than just champion variety. Games are still hinged too much on who has the better jungler, but that's just my opinion.