Well, that's was very good indeed!
I agree that the OP wasn't all that bad. I could listen to it and not cringe, so I am not sure what you guys disliked about it. It's not my top song, but it's certainly better than most of the other stuff we get. Animation is rather well-made as well.
As far as the show itself, it was as interesting as you've said. I wouldn't necessarily put this as the best show of the season, but it's definitely in the top 3 along with The Tale of Two Haruhi's. 8) The story is definitely the most promising one, and I am even more uncertain that this is going to take just 11 episodes. It looks to me that this is not set in stone and the website could be just inconclusive (it didn't acutally say: 11 eps max).
Hajime Mizoguchi is one again excellent with his cello playing. Pay attention to the scene where the brothers are landing of the Chimaera, it's simply breathtaking.
Animation seems to be good, background art varies a lot and is quite inventive (the planet itself looks like it was designed in depth and with lots of different beautiful locations to stage action in), artwork is consistent and so far I like the character designs. The two brothers look like they had extensive work done on them, both by the charadesigner and the scriptwriters, as they are both very well fleshed out. We get to see both their personalities, motivations, abilities. I hope this doesn't turn into "One brother goes on a quest to save another", but judging by some of the future episode hints, this isn't what we should expect in the long run (maybe only in the next few episodes).
The only weak thing that I would name is the illustration of the "generic badguys". They do look rather generic, with similar clothing, hairstyle, look, etc. Not much variation here except for maybe one who have a speaking part, and they don't look that much more inventive either. It's not terrible, but compared to the brothers, their designs look especially lazy.
So, this is a definite keeper for me. Great animation, promise of a great story, AMAZING music... Thanks, BONES, you never disappoint me (and we'll forget that Mars Daybreak thing for now). 8)
BTW, I am surprised you didn't mention that this is NOITAMINA show (Fuji TV josei slot, previously had Hachikuro, Parakiss and ayakashi). Now I am positively here to stay. 8)