IMHO, at the end, the series went full circle. Its theme was stated by Claes in the first episode: "Young fella, enjoy your youth" (as per ANBU's translation). Those girls suffered terrible things after and before joining that damn Corporation, but they should still be able to find joy, happiness and comradery, even if it's just temporary. Of course, it began with stargazing, and ended with stargazin, too.
Secondary theme would be that, no matter what happens, what you do or become, nobody can steal your humanity.
Count me in among those who think Ange is dead. At least, she died peacifully and with Marco at her side. You can't use the manga to prove she's still alive because most of this episode happens early in the manga. The animators changed the order. Ange's story is told later and she's, naturally, alive.
I still want to know what happens to the remaining girls (althought it probably will left me scarred for life). Nevertheles, I'm happy I got to see animated this, my favorite story from the manga. It was very nice to see a story without violence (but still, death was present). However, I'm a bit peeved because
2) We didn't hear all the girls actually singing
Who else thinks it was nicely ironic that a hymn about joy as a most exalted feeling that shoud embrace all mankind as brothers is sung by a group of remorseless, merciless killers? That a hymn originally about liberty and freedom instead of joy, is sung by a group of brainwashed, conditioned creatures being manipulated like puppets by their supervisors using the unbreakable strings of honest and sincere love?
With the rather open final, I can be in perpetual self-denial, telling myself that the girls didn't meet their sad ends, that they continue living and finding laughter and bright days whenever is possible. They will never die, rather, they'll sail into the sunset like the legends of ancient times.
Yes, I'm very moved by the story of those poor girls who, in any other circunstances, would have become wonderfully nice people. I still want to think their souls remain pure and unsullied, even if their hands are red in blood.
Well, it was one hell of ride, one of my most favorite Anime of all times, a class on itself with their design, music and setting. So full of unforgettable moments and memorable characters.
Triela will live forever, at least in my memories she will.