Intellectual rap focuses on two aspects: Concept and Experience. Concept means thought, and many a times these rappers will just rap about whatever's on their mind, making sure that they sustain a smooth flow, and (sometimes) make somewhat of an effort to censor their opinions. The same goes for experience, when they rap about what life has done to them in a detailed and sensible manner.
As mentioned before, intellectual rap isn't as popular as it was when it had its debut at the dawn of the hip hop scene. Nowadays, people rather listen to fake gangsters who try to act like they're hard, when in reality, they speak of false gang memberships (ex Lil Wayne), excessive drug usage (ex Young Jeezy), open-door promiscuous behavior (ex Trina and Yung-Joc), obvious hypocracy (ex Snoop Dogg "wanting less violence" yet constantly still claiming Crip), and other things.