Combining Will Smith's friendliness with St. Louis slang and a down-home drawl, Nelly has mastered his own brand of crossover appeal. On his fifth album, he mostly sticks to that pop-rap formula, cranking his distinctly melodic flow to hyper-speeds and playing the good-natured hedonist on cuts like "Party People." But when he tries to come off hard on a handful of Dirty South brawlers, he ends up...