So let's first praise Holler If Ya Hear Me (*** out of four stars) for what it's doing -- acknowledging that Broadway audiences are growing more diverse, and encouraging that growth -- and, just as important, what it isn't doing: milking nostalgia...Under Kenny Leon's vigorous, sensitive direction, the principal actors -- among them a coolly charismatic Christopher Jackson and a typically warm, fierce Tonya Pinkins -- are convincing and sympathetic, and Waters and choreographer Wayne Cilento mine the robust grooves and soulful nuances in Shakur's material in exhilarating production numbers. Though there are sobering twists -- and contrived ones -- the overall effect is uplifting. By celebrating its subject's creativity rather than exploiting his legend, Holler sets a fundamentally positive example for a problematic form.