Transitioning. Turned me from an empty husk of a person suffering from depression with a nothing life who was just going through the motions into someone happy, with a million hobbies and endless thirst for life.
Even when I understood what GD was and how it was affecting me, I never expected just how much there would be to me once that dark cloud has been lifted, especially how much changed once I started passing well enough I'd be gendered correctly all the time. It was rough to DIY hormones as a teen, but 10 years later, I feel truly blessed.