I've played Kennen in most of my ranked games and he's my main. He's definitely one of those tier 1 champs who can carry any bad, QQing players on your team.

Pros
-High damage that scales through entire game
-Great escape and initiate mechanism (His E)
-He's a ninja and looks like Pikachu

Cons
-Extremely vulnerable to CCs

Skill sequence

E through the minion wave and W -> Profit.

Always try to initiate fights as Kennen. With his E charge into the enemy team and ULT every single champ in their team, following up by a W. Survivors? Q in their face and finish them up with an ACE.