There is a number of criticisms levelled at rap or hip-hop music, with some of the biggest being: "It's all misogynist and violent", "It all sounds the same", "It doesn't take any talent" and of course, "Rap isn't music". As hip-hop has informed the mainstream, you will hear less of these criticisms, but all of them will still come up.
The other criticisms all have their own answers, but towards the complaint that "rap isn't music", the answer should be "of course it isn't". How far rap is from the world of music can be considered by thinking of first, how many famous rock stars, even ones known more for their star power than their musical ability, have embarked on projects working with musicians in the fields of jazz or classical music, and proved that they were also skilled in the field of music. If you look through the ranks of the hip-hop greats, you would be hard pressed to find a single MC who was known for mastering the technicalities of music, or for creating memorable, original music.
So, are the detractors right? Is hip-hop just a pop fad, playing to the egos of the young and confused? Not at all! Just because rap isn't music, doesn't mean it isn't art. If we go back to scanning the ranks of famous MCs, we do see another field of art they succeed in: What do Ice Cube, Ice-T, Queen Latifah, Tupac Shakur, Mos Def, LL Cool J, Saul Williams, Will Smith, Shaquille O'Neal, Eminem, Method Man and Red Man all have in common? They have all had some amount of success in acting, and for many of them, their success has gone beyond playing roles in niche movies trading on their rap status. Although the world of Hollywood movie making doesn't always allow us to see actors' real artistry, anyone who can act in three or more films is obviously talented. And there is obviously a lot of talented actors coming out of the world of hip-hop.
The reason for this is, is that being an MC isn't about music. It is about performance. While some people might think music, which is about the mysteries of why the human brain reacts to abstract acoustical properties, is more of an art than showmanship, I don't think many people would question that being able to perform for people takes a lot of talent. Being an MC is about, first, forming an energy, getting yourself into a mental space, and second, about being able to transmit that energy to someone else. When you hear a rap song, that is what you should be judging it on. And next time someone tries to tell you that rap isn't music, just respond "of course not".