I did prefer Eminem's older songs, The Marshall Mathers LP was his best in my opinion. However the reason he's rapping differently now is because he's grown up, and he doesn't face the same challenges and problems that he used to. If he still rapped about what he used to rap about, when it has nothing to do with his life's current situation, then he'd be fake.
His new stuff is still really good, but they're shadowed by his old stuff. Oh well, he's working on a new album so let's hope that'll be really good.