The way I see it, Vikavolt has a lot of potential that could make it a huge threat if it gets buffed a little more down the road, but in its current state, it's not as good as everyone wanted it to be. 145 Sp. Atk is very exceptional, especially for a Bug type, and 77/90/75 bulk is respectable, but 43 Speed is rather slow for what it is, and while Agility mitigates the abysmal speed a fair bit, it can't outspeed too many threats, even at +2. This makes Vikavolt a bit less threatening, despite its massive power. The lack of coverage, which is to be expected of Bug and Electric types, also makes less use of Vikavolt's awesome power, and outside of moves like Energy Ball (for Rock and Ground types), Mud Shot (which, despite being an answer to Steel types, as well as a way to lower the opponent's speed, is rather weak), and HP Ground (which is the only answer to both of Vika's weaknesses, and takes care of Steels), it's pretty slim pickings.
Right now, I'm gonna wait and see how Game Freak treats Vikavolt in later games, because he looks awesome, and he has more than enough power to be a threat, but the lack of speed and coverage cuts into his effectiveness. I mean, give him a speed buff or the Speed Boost ability, give him Earth Power, give Vikavolt something to make him a better mon than what he is now, eh?