He is by far the best Eminem is an utter genius. Firstly his flow is far better than pretty much any rapper I've heard. Too many rappers these days don't connect lyrics like Eminem does and they simply find things that rhyme which makes their lyrics unconnected. This makes listening to him compared to other rappers jaw dropping. Also, he talks about powerful topics which move the listener and are miles more interesting than the classic 'gangster' style. His style gives him a wider audience which changed rap. Finally, he doesn't simply try and rap fast (with the exception of rap god) which is good because rap is about the words and how they are said, not how fast you are saying them.
