People generally label Haibane Renmei as one of the best slice-of-life anime ever made, but that's selling it short. Sure, there's not much physical action, and much of the series is devoted to the day-to-day life of the title characters: mysterious winged men and women called Haibane who work odd jobs in the walled town of Glie. There are happy moments and sad moments, mysteries that are never fully explained and a cast of likable characters who are all more flawed than they appear at first glance.
Where Haibane Renmei differs from its slice-of-life brethren is that there is pain. Granted, there are elements of loneliness and transience in many such works, from the graduation at the end of Azumanga Daioh to the post-apocalyptic finale of Yokohama Kaidashi Kikou. But in Haibane Renmei, the pain is raw, and real. Wings protrude from backs in bloodstained moments of birth. Fears lurk behind the eyes of those you least expect. At around the halfway point the happiness and light fades away and the show dives deep, dredging up the insecurities of its two main characters with a firm hand. Executed poorly, the shift in tone might have sunk the show, but instead the switch elevates the show to an even higher level without any pretension.
At times, Haibane Renmei is calming and bittersweet. At other times it is heart-wrenching and profound. Sometimes it can even be all four at the same time. With its slow pace and inscrutable atmosphere, the show probably isn't for everybody. But even though it is difficult to find these days, you should seek it out and watch it through at least once, just in case it's for you. It's among the best anime ever made, and there is absolutely nothing quite like it.