Redman/Busta Rhymes/Eminem
in that he's a damn good rapper, but as an artist he's eh. He tries harder as an artist than a lot of the other rappers that are just good rappers, and that shows (his attempts are rarely ever complete failures, they're just "alright").
While Redman and Busta Rhymes need people to produce good LPs for them (both of them seem to only make songs that are as good as the beat lets them), and Eminem needs a friend to tell him when his shit is actually fuckin' weak, Nas seems like he needs a good executive producer. If he had the vision/production level of MBDTF he'd easily come out with an album that people remember as well as his first two.