Eminem is too talented, to retire in my opinion. He was a White Rapper with better skills than I'd say hm, 98% of the rappers in his modern times. He broke stereotypes even under resistance. He also knew better than to fuck with Canibus. Alot of people hated on Eminem, so that just shows how great he was at what he does.
I'm not as much a hip-hop fan as I was growing up. Maturity hit. I didn't listen to much of Em when he wasn't being goofy. But Mainstream Rap music doesn't allow clowns(ICP is not mainstream), so he was hardcore as well, and did a good job at it all. The fact he has a sense of humor to his lyrics will make it timeless. Canibus is often called too heavy(i don't think he really cares too much about fame or fortune or what anybody has to say) - so its harder to listen to Canibus. he doesn't grab your humor, or your emotions, as much as he grabs your brain. Eminem, and Canibus are able to amaze.
