He is quite strong, if not OP for a champion that is underplayed. Other than a HUGE mana drain stun for early lvl's.

He has a spell to boost his ad and maximum hp (if the spell is active and he last hit a minion) which is incredibly good early game for harass and burst with the stun.

His shield is quite amazing to, does damage or can absorb damage.

Now here is where I would think people would be crying pretty hard about Sion, his ult. A 30 second sterroid that increases his attack speed and life steal by 50%. If your building AD, you can EASILY survive a 2v1 if not a 3v1 till your team arrives, IT'S THAT STRONG. I have done 2v1 situations when not fed and at the same lvl as everyone, running off the tankiness of that ult.

What do you guys think of Sion?

He will be a champion I will try when avalaible free. I play VS him and he was getting lot of kill's like Darius do. So I guess he is very strong but tricky to play. The, maybe, why not much player's play him.

I play Gragas as well, he is great but I NEVER see someone play him so far...

He is extremely easy to kite. Melee auto attack champions are generally lacking a place in the current meta

problem with sion is he's got half half spells with 2 on ap 2 for ad, aside from his stun he's got no utility or ability to chase meaning u'll almost always end up getting a frozen mallet or some kinda slowing item on him and there's so many champions who do his job better. mundo and olaf are probably the most prominent examples and they're both alot more popular for a reason.

Sion is too easily countered, no escape, and no offensive abilities unless played AP which makes his ult less attractive (if playing AP). If the team doesn't have lot of CC / Exhausts then he can dominate. However, ignite and exhaust > him as AD. As AP his burst is fun but since he has no gap closer other than is single target stun he's better in ARAMs than normals .

Don't get me wrong he's fun and can snowball but he's not a serious champ because he is too easily countered like AD Yi imo.