Cho'Gath is under rated and awesome
I'm not sure why he doesn't see more play. I don't think i've lost a ranked solo queue match with him yet (9-0). I have lost a few 3s though. Granted I usually only take him into favorable match ups, but he really doesn't have too many unfavorable ones to begin with.
I think what makes him so incredibly strong is his level 6 ult vs monsters. 1k True damage? I very rarely miss out on securing dragon / baron in the first 20-25 minutes of the game. The enemy jungler has almost no chance when I have ~500 more true damage than them.
The man is solid in lane with his sustain. He murders champs like Zed, he has a strong AoE silence. Oh and you can take him Top / Mid / Jungle pretty easily.
Cho'Gath is beast mode.