Very few people have any grounds for criticizing Aseop Rock's rapping. He is an artist in the truest sense of the word; his style is so perfectly and consistently realized on this album that taking fault with the sound of his voice or the quality of his beats is stupid. It will take you several listens to even begin to get into some of the incredibly crafted metaphors this guy spits at such an incredible pace.
But I do have to complain about some of the production. Some of the beats Aesop Rock does himself are little more than functional. They are all pretty understated, and some of them (Spare a Match, Big Bang, blockhead's interludes) are great. But the best songs on the album are ones like Basic Cable, Commencement, and Oxygen, where the astonishing and engrossing mic work makes it so that you won't notice the beat at all. Especially Basic Cable, which is deep and easy to relate to at the same time, and may be the best one on the album.
So to recap, if you're like that reviewer everybody else is complaining about, keep listening to above average rappers like Nas and Jay-Z and don't bother with anything deeper or underground, which is NOT ABOUT THE IMAGE but about the art instead. But if you like music that has an aesthetic reason for existing, then get into Aesop Rock (maybe his later stuff which has better beats) and other people on Def Jux.