Can we talk about Kassadin for a sec?

Kassadin is an interesting champ, to say the least. He has AP scaling like a mage, but he has mobility like an assassin. But when it comes to raw burst, Kassadin simply cannot compete with other assassins. Even before they gutted him, Kassadin was never able to outburst someone like Katarina, Fizz, Leblanc, Talon, etc. So what we end up with is a champ who needs to build like a glass cannon in order to kill anything, but he isn't rewarded for doing so. So a Kassadin player has two options. You can either build somewhat tanky and have less than optimal burst, or you can build glass cannon and still have less burst than other assassin champs.

I would also like to point out that unlike other assassins, Kassadin has clear weaknesses during all stages of the game. Even Akali, a champion who is supposedly "weak" pre-6 has access to stealth at level 1, so one could argue even she has an easier time surviving laning phase. He doesn't have access to his mobility until level 6, so you have plenty of time to retaliate after he bursts you. And again his burst isn't that great, so most mids can easily beat him. Even after he gets his ult, you have plenty of time to retaliate after he bursts you. Unlike champs like Zed or Leblanc, Kassadin cannot immediately return to his starting position after he jumps in on you. His ult is also fairly expensive to use, so if he doesn't have enough mana he's out of luck.

Like so many other champs before him, I believe Kassadin is a victim of "FOTM syndrome". For a time he was extremely popular. After a while people started complaining, and Riot proceeds to gut him. But I think Kassadin deserves a second chance. It's a new season, with new champions and new items added, so maybe Kassadin won't be as obnoxious as he was in the past. If he isn't buffed in some way, I don't see him being played much. He simply isn't strong enough to compete with other top tier mids.