Even by that standard, 'Summer: The Donna Summer Musical,' which opened on Monday at the Lunt-Fontanne Theater, is a blight. Despite the exciting vocalism of a cast led by the formidable LaChanze, it reduces the late Queen of Disco and pioneer of electronica to a few factoids and song samples that make her seem profoundly inconsequential. You could learn more (and more authentically) by reading a thoughtful obituary while listening to her hits - 'Hot Stuff,' 'Last Dance,' 'She Works Hard for the Money,' among many others - online.