I don't agree with Cali, however I DO Agree that 50 cent, Lil Boy, Etc. ARE in fact hip hop.
http://www.youtube.com/watch?v=iWa4UpajKTc
Nuff' Said.
Listen to what he says about "Hip" and "Hop". If you personally don't enjoy mainstream music don't listen to it. Just because someones rhymes is iller don't mean that they're more hip hop than you. Everyone does everything different. Some people enjoy other styles. I listen to both Mainstream and Underground hip hop, why? because it's all hip hop. If it sounds good, TO YOU, listen to it, if it doesn't, turn the song off. For instance when i'm chillen sometimes I like to throw on some Nas, sometimes I'll throw on something that bangs. But both Commercial and Underground music reflect different moods.