Impressed with both of you right now. Gangstarr is my shit, listened to full clip in its entirety earlier today. Theres SOOOO many better rappers / hip hop artists than the ones mentioned. I mean im not knocking the rappers mentioned by OP but most of them are known for their individual flow or hooks not really for their lyricism.
Either way... gurus got all that shit in spades and doesn't put up some uber (fake) gangster front.
Some great guys that should have made the list (that haven't been mentioned yet) are:
Q-Tip
Del/Deltron
Mos Def
Scarface (not exactly a lyrical genius but great flow, better than Big Pun Eazy E and Big L easily IMO)
Talib Kweli
Phife Dawg