I love Starlight.
It has been truly satisfying to see how much she has evolved since her debut. She has always been highly intelligent and motivated, with magical ability nearly equal to that of Twilight. It was sad to see how a traumatic event in her life led her down a dark path towards becoming a hard line idealist and a control freak. Her self-injuries nearly destroyed her, along with all of Equestria, but fortunately she found her salvation and has continued to experience tremendous personal growth ever since. Her true potential has yet to be fully revealed.
Eyes open wide, she is willing to learn and readily owns up to her past mistakes. She is perfectly imperfect and remains controversial in spite of her efforts to do good. Through her unique experience, she was the only pony who could see The Pony of Shadows as lonely and misunderstood, and vilified by his own heroes. More and more she continues to be a positive influence on her friends, especially Twilight.
Redemption & forgiveness have been key themes for FiM since the beginning, and I believe that the creative staff for the show really wanted to bring this message to the forefront with Starlight. In a world where many people want to see things as black or white, it is refreshing that a show like FiM doubles down on its colorful portrayal of (ex-)antagonists.