I liked a lot of Enimen's works such as "Stan", "Loose Yourself" or "Criminal". I liked the flow to his rhymes, the lyrics (partially), beats, changes, energy conveyed, etc. Stan in particular, despite having been played at least a million times on radios, is one of my favourite hip hop tracks. He might no rap as fast on this track as your average rapper would but if speed was a definite criteria for lyrical accomplishment in general than poetry slams would fail according to these criteria.
Anyway, I haven't been too much into his latest work because there was hardly anything new and my musical tastes have changed but nonetheless, "Marshall Mathers" was a really good CD in my opinion. Perhaps he doesn't sound like some of the other respected hip hop artists but that doesn't make his work any worse just because he lacks conformity to the supposedly higher standard. What I also don't like are those "funny songs" as Ttvetjanu already mentioned but hey, your mileage may vary. The refrain on "Criminal" has an excellent flow to it and there's something smooth about the way he accencuates his words in the chorus.
Edit: However, his deragatory attitude towards certain groups of people, although I'm unsure whether it's only his twisted sense of irony, is something I don't like.
And anybody disagreeing with hip hop being music, take a listen to The Roots or Guru Jazzmatazz. These people know more about music than most other people in the business ever will. Still, even the Root's obvious skills of handling their instruments or writing music doesn't make them more of a musician than Eminem because there are no fixed criteria to music as long as there's an audience. You could argue that making an absolute statement on disagreeing with absolute statements presents a contradiction, so just take it as an opinion if you will.
Not liking a particular style - why not; taking a musician apart - sure if it's legitimate criticism (although always to a certain set of criteria); specifying something as not being music, however, speaks of perhaps musical arrogance, maybe overconfidence in one own's musical preferences but certainly reveals the belief in an absolute set of criteria of "music" ought to be. What is music anyway? Going by a popular Indian definition, music is the violation of silence. There have been people calling Shakespeare's poems "music" although these people certainly wouldn't want me using Shakespeare in Eminem's context... Just my opinion.