Personally I think his production abilities are quite overstated. He's nice, always brings something new to the table, isn't scared of experimenting but I can't find myself enjoying it as much as I would enjoy a Kno, Premo or a Dilla beat. He's like the Canibus of production; too intricate for my liking(pardon the analogy).
As a lyricist he's quite underrated but I can't stand his flow and his rhyming abilities are extremely mediocre, so just an above par emcee for me.
He still manages to put out good to great albums and has one of the most impressive discographies in the genre.
Also, what are your favorite songs by him?