FX’s “Legion” TV series is based on a character from the X-Men comics, but knowing the backstory isn’t important. This isn’t another superhero comic adaptation, but something unlike anything we’ve seen before—a visual and auditory feast, great actors, and smart writing that will make sure you sit up and pay attention. If you’ve written off comic-book TV shows and movies, time to circle back and appreciate this eight-episode first season from writer/producer Noah Hawley (“Fargo”). Expensive music! Beautiful sets! And actors who used to be in “Downton Abbey”, “Parks & Recreation”, and “Designing Women”! What more could you ask for?