I think many hold him to a totally different standard( I dont necessarily mean higher or lower just to a different one) than other rappers. When Eminem spits a corny line its the end of the world, but theres countless rappers that do the same if not worse and can totally get away with it. It becomes, "oh you dont listen to this artist or that artist like you do with Eminem." I think it all ties in to what we specifically want to hear from him, and if it doesnt conform to our preconceived notions of what he should be, then we're not happy... Or we're in shock and surprise.
I feel this higher level of scrutiny a lot of us inflict upon his music prevents us from being open to hearing different things from him. Things such as him rapping on a trap beat. As much as I eventually grew to really enjoy songs like "so far.." and "love game" they totally came out of left field to me sonically. I liked them initially, but it took awhile for me to really get into it, because its not what I would ever expected to hear from him. I think for a lot of us he was the first rapper we really got into, and we've pigeon holed him into certain sounds which makes it hard for us to accept other sounds that could be equally as great. Im not saying he's always successful, but we seem more resistant to Eminems experimentation than to say Kanyes, or Jays. This obviously wouldn't always hold true, just when it deviates too far away from we expect from him.
I hope Im making some level of sense here lol.