He actually is a common pick atm. Despite his avg win rate, he's very popular, placing him at a top tier pick among players.
As for what he is, he is a self-sustaining lane bully. He's quite capable of taking out half your HP bar with one combo. After the second combo, he usually ignites you for the guaranteed kill.
As for how to deal with him.
Legend: Tenacity/Unflinching Runes can help with his stun as well as getting Mercury Treads early on. Bonus Armor stats from your runes will also help mitigate much of his early damage.
If you are in an unfavorable match up then Doran's Shield might help you with sustaining his pressure in lane.
Otherwise, read up on his skills online to get a better understanding as to how they function, especially when empowered by his passive. And memorize his cooldowns. This will inform you of his weaknesses and when and where to exploit any and all openings he presents to you in game.