I'd take great passion over the "best lyrics" any day. That is why Tupac is one of, if not THE greatest rapper ever *personal opinion* Due to the fact he may not be the best lyricist, but the passion he brings to the music MAKES you relate to what he is saying... even if you can't necessarily in reality. Kanye, despite his antics, brings passion and he has some sick rhymes in some songs as well
Edit: Trust me, if the rapper doesn't have some swag *which jz does* Then hes not that great, and voice plays a great deal in keeping interest for me.