Easily the most overpowered champion in the game right now.
Mixed damage means you can't build defense against him.
You can't run from him, since there is virtually no cooldown on his hop.
You can't have your ADC kill him, he'll dodge it all, stun the ADC, kill him easily, and Jax is naturally extremely tanky even without his dodge.
If his team is crap, he just backdoor since he can easily rape a tower in a few seconds.
His scaling is the most absurd thing about him. If you make it to end game and the enemy team has a Jax, you automatically lose, period.
There is just no effective counter to a Jax.