as an overview, I would have to say the most important things are a combination of lyricism, emotion, and overall song creation are the three most important things for me when judging an artist. Lyricism holding slightly more weight but I enjoy artists who are able to bring across an emotion in a song and who aren't scared to do so. Most of todays artists who are popular have that problem. You don't get anything that makes you feel like Rick Ross has been in your shoes when he raps. Hell, until recently, I would say Ace Hood didn't get it either, then he released Blood, Sweat, and Tears and several of the songs let me know that he gets "it".
Being emotional is not to say an artist is acting like a bitch but that he or she is getting across a certain feeling. Listening to "Get Rich or Doe Trying" you feel 50's aggression and determination to make it or die before he lives broke. That's an expression of emotion. DMX might be one of the best at emoting in the history of hip-hop. Just listen to "Stop Being Greedy" and tell me you don't feel his passion and pain, the entire album is one big exercise in how to create emotions. Even still when you look at his features on songs such as "Why We Die" from the Busta Rhymes album "Anarchy".
My favorite current artist at the time is Joe Budden and that is literally because of his ability to express himself on the track and to expose himself. Many times he drops freestyles about his personal relationships and the way he feels and I know that other artists do so but are too concerned with having the image of being infallible. Here is "10 minutes" from his first album where he just lays out his whole entire life.
To me he might be able to be a top 5 emcee if he could put together some of the other items that I would list when thinking about the best rappers, but two important ones that he has are great lyricism and ability to emote. the number one rapper ever, point blank is Jay-z and he has the best mix of overall talent when it comes to lyrics and song creation and occasional ability to emote. "Song Cry" and "Hard Knock Life" are two sterling examples of that ability.
This is why I look at someone like J.Cole and I just don't believe him. While he can rap, the words he deliver are devoid of any real substance. He knows what you want to hear but he can't let himself loose enough in them to become one with the music. I feel the same thing about a Wacka Flocka and Rick Ross. They may be on the opposite spectrum of topics of a Cole but yet when I hear them, I just hear rap. Just literal words that don't have anything in the way of meaning behind them. Point blank, I know after seeing some of my recent posts including rankings and etc, you may want to know what comes to my mind when we talk about good rappers or mc's. This is just a taste believe me.