Eminem needs to re-invent himself.. That's about as much of a "retirement" as you'll see.
He needs to re-package the product and give it a new spin. He's not angry anymore. How can you stay pissed off at the world when you have enough money to do pretty much anything you want? His anger isn't in the music anymore... at the pace he's going with songs like "Ass Like That" and "Without Me" he's started leaning more towards gimmick rap and horsing around. He isn't taking himself seriously anymore and it shows in his music. He's reached a point where he can basically make fun of anyone he wants and everyone just laughs along. He's not controversial anymore and is quickly becoming the next Weird Al.