I'd hate to get technical on you but it MAY be SORT of blasphemous to say he's a terrible "RAPPER."
It'd be fair to say that he's an average "lyricist"...but to say that he's a terrible rapper would be to say that he's terrible AT rapping, which he isn't.
Pretty good verse structure, cadence, change of flow pattern from song to song, and breath control...all from a guy that smokes a shyt load of herb everyday and can carry his own on the microphone live w/o leaning too hard on a hype man. If you get what I mean and keep that in mind, he can actually out-RAP a lot of people.
Not the most clever or deep cat in the game but he's definitely consistent enough to not be a "bad rapper".
Hope that makes sense.