I hope that Riot is being careful with those Jax buffs...

Jax is currently somewhat balanced, if only because the nerfs to his base stats made him a lot easier to deal with.

Before those nerfs, he was even worse than Riven, because he was very oppressive against many champions; a single mistake meant that he would snowball out of control, and even if you were using a counter, you would have to play perfectly, otherwise Jax would still snowball and beat you.

Although Jax uses mana, he has a low cooldown escape that can also be used as a gap closer, it is almost impossible to 1x1, and can dodge auto-attacks. What made him worse than Riven is that he didn't needed (and still don't need) to build full damage - only a Triforce and a BotRK was enough, and then he could build as a tank and wreck everyone.

And because of those reasons, Jax was one of the very few champs who managed to reach Kassadin levels of ban in draft games. He is balanced now because the nerfs mean that now Jax is easier to deal with during the early game AND during teamfights. He also needs to decide if he wants to start build tanky after a TriForce or build a BotRK. He used to be able to build both without being squishy as a result due to his high base stats, but now if he builds both, he will be very squishy because he will have no defensive items.

Now that he is balanced, I hope that Riot watch out for any buffs that they make on Jax. With the correct buff, Jax can return to be the oppresive and dominant force that once he was.