I think what it's come down to in whether people love or hate it is if they're down with the route he chose to take with the subject matter of most of the songs. I happen to be a big fan of the Slim Shady character, I find most of it hilarious because I have a warped sense of humor, and although I also love his more "serious" work, I don't necessarily think there's any more merit in that than there is in doing crazy Shady songs. Music can be deep and personal and that's cool, but it can also just be fun and still be as awesome. I don't mean "fun" as in Souljah Boy music devoid of all quality, either. The talent should still be there. Now it's just a matter of whether your definition of "fun music" matches Eminem's. If it doesn't, then that's fair enough, but you can't use that skirt over the fact that the dude is still a lyrical beast. Putting your preferences in what side of Marshall Mathers he should have focused more on aside, when it comes to rhyme schemes and wordplay, Relapse might very well be the best of all his major albums (the Marshall Mathers LP and Eminem Show are in another league overall, mind you).
What Eminem said in that "Prelapse" interview pretty much coincides with the impression I got: he's doing the type of music that brought him to the dance because that's what he enjoys doing the most, and no longer is interested in appeasing listeners who feel he's obligated to be serious and mature on account of being an "important artist" as mentioned above. Though he's not completely finished with "serious" music, as seen in Beautiful and De Ja Vu. Who knows what Relapse 2 will bring?
Yeah, maybe twisted stories about killing celebrities and preying on women are old, but are love songs not old? Are songs about dancing not old? It sorta makes me giggle when people call his shtick old hat and then get hard-ons for songs that have the phrase "in the club" in it. At least Eminem is doing something that he pretty much started himself (not to say he wasn't inspired by various artists like every other MC). I think the majority of the work on Relapse is both nostalgic and fresh at the same time, something that Dr. Dre's beats really helped with. Not to mention that everything except Crack A Bottle blends nicely with the theme of the album and the name of the album itself. He really has relapsed on this.