Rap music is often lumped together in the minds of many people. They do not realize that rap music comes in many different styles and forms. People may like one style while they do not particularly care for another. Each style has its own unique qualities and people of all ages enjoy it.
The choice of lyrics is one of the most obvious ways that it is different. Some rappers choose to stay clean and not use any profanity in their lyrics while others are more liberal in their choice of lyrics. Gangster rappers are known for their profanity with groups such as NWA being the forefathers of that style.
Another major difference is how serious the rapper or group take themselves. Groups like Public Enemy or rappers such as KRS-One have meaning behind their words. Public Enemy's song, "Fight the Power" is a classic example of a song that has meaning behind it. Enimen on the other hand, is known for being less serious and makes constant jokes in his lyrics. Enimen often pokes fun at celebrities in his words or calls somebody out like he did with the artist Moby in one of his songs.
These are just two examples of how there are differences in rap music. Just like how some people like different kinds of rock and roll, people like different styles of rap music. There are many styles out there and one should not classify the genre of music as a whole is a big mistake when you consider it all has to offer.