Viktor is a lane bully with consistent poke at below average range, and relatively high poke with lower consistency at above average range. He can function as a poke champ or as a dot champ depending on his skill path and itemization.
Problem with him is that he's pretty shit stat-wise to balance his starting item advantage. However, that item falls off hard and his stats never catch up to compensate for it. Combined with overall poor range and poor scaling on his spells, Viktor falls off hard by the end of the game, usually degrading into a half-support, half-poke ap mid.
Basically, you should play him against people you can safely harass with little risk of retaliation. He does fairly well against Orianna and Akali in early laning if you prioritize Q, and he can deal with most people in laning phase to a standstill if you prioritize E. However, he really has no place in any lane, as much as it pains me to say it. His range is just too short and his scaling is just too low to justify playing him. He had a 100% win rate in challenger for 3 games in the start of the season as a counterpick to Orianna. Other than that, I haven't seen much success on him other than getting really good at the laser and shutting people down with it.
TBH, I'd wait for his revamp. Supposedly they're going to let Viktor get two upgrades on his augment, which would make the item viable and let him scale into late game. Red and Blue are the only good augments right now, so they will likely buff yellow as well. Either way, right now he needs red aug to keep up with damage, but he needs blue aug to make his gravity field anything other than a disengage tool and for the cd.
They could possibly make Viktors augment be his trinket, like they did with rengar's necklace, and let that stat removal from the item give them a reason to buff his range and base defensive stats to let him become a potent duelist and lane bully who becomes a consistent dot mage weaker than ryze in the late game but with more support capabilities.
I would prefer the latter option, as he was designed to fit the season 2 meta more than the current meta, and his skill set is sorely outclassed because of it.