I think his lyrical sense of meter and time are great and his clever use of rhyme and half-rhyme excellent. But his lyrical cleverness can get a bit cloying as he is constantly self absorbed and self referential.
I get a bit tired of listening to the banal but self aggrandising anecdotes of his life and his mom etc.
However, compared to some other rappers he is modest mouse. I find constant boasting about sexual conquests and/or willingness to beat women/kill rivals very tedious.
Interesting that the best racing driver, golfer and US President are black guys but the best rapper is white. What happened there?