Janelle Monáe likes to hover outside categories, with a sound and a look that are both visionary and retro, steeped in OutKast-style hip-hop while hearkening back to Cab Calloway and Fifties doo-wop and James Brown. Her full-length debut — about a robot-populated utopia based on Fritz Lang's classic 1927 film Metropolis — is so ambitious, so freighted with sounds and ideas and allusions, it threatens at times to sink under its own weight. But on ferocious songs like "Come Alive" and the manic neojump blues "Tightrope" (featuring Big Boi), Monáe's charisma and energy are so forceful that the jumble makes perfect sense. Whoever else — whatever else — Janelle Monáe is, she's a star.