I thought the first season of this anime was good and entertaining but certainly not anything to write home about, a slightly tropey anime with interesting character work and a novel setting.
The second season did something that I (to my recollection) have never seen in an anime, and rarely see in television writ large: a complete re-examination and re-declaration of the show's thesis. It was slow, atonal, and deeply penitent: it was an incredibly rewarding and rich meditation on freedom, violence, and the human condition. Absolutely blown away by the work done, and I found myself both deeply satisfied in the show's narrative arc — by all accounts a complete success — and thrilled by the prospect of a third season.