Opera should be a direct, emotional, moving experience: I say it all the time. So it would be churlish — even contradictory — for me to carp at the Wolf Trap Opera’s production of “Roméo & Juliette,” Charles Gounod’s operatic version of Shakespeare’s play, which will have its final performance Saturday night. Led by the radiant acting of Madison Leonard as Juliette, the young cast delivers a powerfully affecting and emotionally riveting performance.