Yeah, I actually play "corrupt" warlock without Yshaarj simply because some of the corrupt cards are rather good. It's only an issue against priest. The only deck I have with him now that is any good is quest control highlander shaman which uses him as a combo finisher.
I think he's fine, if anything they missed the mark with the other old gods. C'thun's spells aren't good enough so they dilute your deck. Yogg is too random, great sometimes and nothing other times so it's hard to justify the 10 cost. and the menagarie build just doesn't seem to be good enough, more menagirie support needed, though I'm not convinced it hasn't been found yet.