Honestly, I like most of Cho's kit. The theme of Cho'gath is basically playing Godzilla -- once you scale, you shake the earth and literally eat other champions for breakfast. Dealing with Mundo (the Hulk, obv) inspires disbelief. Dealing with Cho'gath inspires terror.
So personally I'm happy with both Q and W as terror tools. They're unwieldy, but they're huge CCs, viscerally and in terms of how much space they actually control. The things that really don't fit are his E and his passive. I'm really not sure what his E is for -- I mean, it makes his trades scale with AP and gives him a little more waveclear, but I don't really see why he needs those things. And his passive is just another lackluster sustain passive, one of the worse ones.
Here's my Cho rework:
* Reduce the AP ratio on Q. Q's AoE size starts smaller than it is now, but scales in size with Feast stacks.
* Instead of its current behavior, E is basically Kayle's E, with no range boost. While it's active, Cho's melee attacks do AoE damage around the target and have an AP ratio. AoE size scales with Feast.
* Remove or reduce AP ratio on R. (To keep mage Cho from getting out of control.)
* His passive does...something else. I dunno. Either something to keep him in lane that is a little more interesting (and mana-effective) than "last hitting is good", or something to make him really scary to stand next to in teamfights.