I really hope this actually means something but Kassadin 
needs a buff. He really needs more damage and his silence back...and more distance on his ult. I actually feel like crying when I want to play him( due to pure nostalgia). Please Rito you're my only hope!
Revert to season 3!
I think he's fine rn, i had no troubles playing him after his changes. He definitely doesn't need his silence back, assassins with silences has been proven to be cancer (hence why all assassins had their silences removed).
You do NOT want him to have his silence back. Not in the current state of silence.
Well , I find him a good champion , with an unique play style. Despite the fact that his buff/nerf history tends to say he was gutted , he actually has significant buffs to his core items , and entirely new options of build paths.
Rod of Ages offers more AP and mana at the exchange of a few HPs. Archangel Staff got buffed by a noticeable amount of AP , making his tear build pretty good. Luden's Echo traded AP for more mobility , helping Kassadin to roam more easily without his ult.
AP item's rework gave Kassadin a lot more toys to play with his enemies.
As a side note , has anyone tried going triple Doran's Ring on him , instead of crystalline flask with components of catalyst? Just try it , and you will find that high scaling abilities aren't good only in the late game ;)
All I can say is that as a Kassadin , you should adapt to every situation. You have the choices between scaling into a late game monster ( Rod of Ages rush + Tear of the Goddess ) or a mid game Assassin that has the potential to snowball the whole game ( Doran's Rings + Luden's )
I personally found it great to have two Doran's Rings , then you can easily sneak a Tear if you get ahead , or just build Rod of Ages, and then what you need.
Honorable mentions:
Ionian Boots of Lucidity: sometimes having your combo ready more often can help you more than higher damage in one rotation.
Abyssal Scepter: do you have a hard time vs magical damage dealers . Maybe you need some more penetration(damage)? This item can help you.
Haunting Guise: good for extra penetration and HP. Also , its upgrade can be good vs bruisers .
Rylai's Crystal Scepter: good for chasing targets, gives a big amount of AP and Health , and can be good at helping your teammates kite.
And many more items that every mage buys them , or have synergy with his kit(Sheen items for example).
New tentative changes for Kassadin in PBE !
Nether Blade [ W ]
Cooldown decreased from 9 seconds to 7 AP ratio on active increased from 0.6 to 0.7
