I like Sion, but he needs just a little tweak.

I feel he is just a tad too slow. No item should be mandatory for a champion, however boots of swiftness (+upgrade) nets him ~420 speed. That's horribly slow compared to practically everyone else.

Even if you hit him someone with E, the chances of closing are very, very slim.

Just a little bump to speed should do it.

His W (passive) -- big monsters + champ should be 15 HP. Make the +2 HP +5.