Rhyme and reason: the Eminem vehicle 8 Mile offers a surprisingly gritty ride. (The Critics Film).

PART OF THE rUN OF 8 MILE is guessing at who's in the lead role: Is it the real-life Marshall Mathers III, the sullen Eminem or the explosively perverse Slim Shady? Starring Mathers, aka Eminem, aka the most controversial white boy in music today, 8 Mile teases us with its billing as a semi-autobiographical account of the rapper's life, suggesting that this might be the final word on what makes Eminem so confounding, so fascinating and so enraging.

But this being Eminem, we don't come away with much biographical insight. After all, the rapper has as many stage personas as a ...