I haven't played too much soon but I have noticed a LOT of people complain about him ever since his rework and here are some buffs I think might help out a lot. Reduce the time it takes to fully charge his Q, make his ult do full damage at a much shorter range. Make his ult easier to steer and harder to dodge.
Sion's E deals a ton of damage and he becomes super tanky quite easily. Yes he is extremelly harder to play than before his rework, but his effort-reward became higher as well.
I just think that, if we are to buff something in any ability of his, his insane bullying tool might need to be toned down, which is something I wouldn't want because its his only way of surviving against ranged top laners.
To me, I think we are looking at a champion with somewhat decently defined strengths and weaknesses.
build like a brick to a shit ton of dmg and cc.........
http://www.newsoflegends.com/index.php/pbe-round-up-patch-5-4-35082/#6
He might actually see some nerfs next patch due to his strength and popularity
The new Sion is pretty widely know for his heavy CC & natural tankiness, not for the damage. He is fine as he is now.
Passive- Looks way cooler than the old Sion ult. At least you can have your own revenge whenever someone kills you, then you kill them back. In situational times, it works really well with 
Q- A very good AoE CC to heavily disengage an enemy team. If your Q is interrupted, meh, you receive like 80% cd to cast it again.
W- My favourite :) HP stackings are so addictive, that I just wanna stay in my lane & cs 24/7, except if you go against champs who deals %HP damages like 
. Shield is also pretty good for counterpokes & pokings for yourself
E- The core damage for top lane Sion. At max ranks, it seriously hurts a lot on squishy targets, but Rito has planned to nerf it on patch 5.5 by increasing its mana costs.
R- The best disengaging tool besides his Q. Works best if you're up to the enemy's face to do it, since it's easier, & it offers the same amount of knock-ups. Also a good tool to get into teamfights from afar.
