Just a few notes on a review:

Over my years of browsing anime forums, I’ve seen that there is generally a pattern in terms of how people respond to “Haibane Renmei”. There is one group of people who have watched the series and rave about it, ranging from calling it exceptional to deeming it a masterpiece. Then there is a second group of people, who always reply that they dropped the series after a few episodes, and found it uninteresting.

This is not unique to Haibane. How many people dropped Gurren-Lagann at ep.4?

It’s quite a unique series. It brings you into a strange setting but does not go into detailed explanations about what or where this setting is.

RahXephon does the same thing — to talk about series which excel at it.

The concept of sin and forgiveness plays a major role, but no direct references to any religion are made, although the angelic wings and halos have clear implications.

Don't forget that Christianity is an exotic religion for Japanese, not known well by most. By necessity, ABe has to refer to the erzatz Christianity in his imagery, not the real one.

BTW:

The opening theme is called “Free Bird” and is a wonderfully bittersweet instrumental theme, which is a wonderful break from the pop music that usually opens anime series, and would have been completely out of place here. The piece revolves around a melody played over a repeated chord progression, I-v, that is, a major chord followed by the minor chord of the fifth. Here is G major followed by D minor, repeat. I only mention that because I’ve always liked this chord change because it has a lot of nuances that can be manipulated by a composer to reflect sadness, joy, and as in the case here, a nostalgic, bittersweet quality.

Pro.