Well, from what I've heard (I haven't been able to double check this since I don't read Japanese) apparently the show changed from a more, monster-of-the-week approach early on (with Naru being a prominent character) to what we got which was more connected to the original series and, given the strange difference between the early promo art/first opening and what actually happened I'd believe it. I am happy that it wasn't just monster-of-the-week but I don't think it was a good call to apparently re-write the entire story just weeks before the broadcast start.....
Eureka Seven: Astral Ocean
Summary: Ao has never known his father and his mysterious, turquoise haired mother vanished years ago in a scub burst. So he's grown up on the semi-independent island of Okinawa shunned by just about everyone but his sickly friend Naru and, through a slightly complicated series of events, ends up piloting his mother's old mech to save the island and becomes closely entwined with the eventual fate of the world and it's fight against the secrets and the scub.
The Good: When the show is firing on all pistons it's a really great show, for the spring and summer it and Hyouka were the two shows I was most pumped about. Ao is a sympathetic character, like the viewer he's caught up in the growing, changing politics and (since for the majority of the show even veteran viewers had only theories on how the two shows were connected) there really is no easy or right way out in this show IMO. The side characters got a bit more fleshed out than I expected, the show showed off more of it's setting than I expected and it did do one of the better versions of a parallel universe that I've seen. I don't think it's a spoiler to say that, since you say a series is a sequel and it's set 10,000 years earlier it's logically got to be something like that, and it actually explains how that happened and puts the viewer in the interesting position of knowing that the "real" world (ours/the one that the people in the original show left and came back to) is out there but wondering if that's really what the characters should be aiming for. I imagine most people didn't care that much about that detail but I really liked it, now if only they had actually answered that question in the end....
The Bad: The show reached it's peak towards the middle of the series and it's not like it skyrocketed downhill from there, it got really confused and it only became apparently in the last few episodes (especially the last two) that it just wasn't working. The short version is that the show took all of the themes that were so important from the original series and tossed them out the window by ignoring them/having the characters destroy them, the long version was eloquently written up by some of the users on tvtropes (especially the 10th post down, number 510, spoilers for the last two episodes apply to the entire page but everything should be behind spoiler tags). I'll admit, I'm biased against series where to create a sequel they have to undo what was supposed to be a happy ending in the first series (as opposed to a show which was always meant to have a sequel and this was always the intent) and again, in doing so the writers ended up contradicting all of the themes from the first show which just didn't work. I had some trouble with some of the other subplots, I feel like they changed whatever was going on romantically with Ao at least twice during the show, Elana's bit was dragged out too long (not a lot too long but long enough and it was really confusing at parts), and both Naru and Truth didn't quite work in the end (which is an understatement for Truth in my opinion) but I was still okay with the show up to those last two episodes, now I'm confused about how I feel and just generally unhappy that whoever was in charge of the writing thought this made sense and made for a good story.
The Audio: As far as I can tell, ANN isn't being really clear here, the musical team behind AO is not the same as the team behind the original but damn the music is still catchy none the less. I do question some of the music (like the second ending theme, is it just me or do shows these days love to have catchy outro music when the show gets dark?) but hey there were some parts in the original show that I really questioned as well. The voice acting was pretty good, Ao was even voiced by a teenager which gave his voice some nice rawness, although there was one casting decision I questioned. I probably shouldn't say who it is but again, it's from the last two episodes and if you've seen E7 recently (and in Japanese obviously) you'll know it when you hear it and I really didn't like it, although it does fit in with the destruction of themes if you think about it in a sideways kind of manner.
The Visuals: Like the audio, no complaints here, the show looked fantastic! It was colorful, the mechs looked similar enough to know that they were based on some from the original series (no literally, that's the in-universe reason) yet different enough because they did come from two different groups of people (again in-universe), and the fight scenes looked glorious. The character designs also looked similar to the original series (as far as I can tell neither the character no the mecha designer are the same people from the original show, although it looks like some of the other people who did design did some in both) and the backgrounds were nicely detailed as well. So, like Fam and Korra (hell, did all three sequel shows have the protagonist's name in the title?) this is a show which had amazing production values yet some writers which seemed to have trouble this time around.
I probably should have said this at the beginning but no, I don't think that the original Eureka Seven was a masterpiece beyond words or anything like that and that's not why I'm so hard on this show. I did really enjoy it, especially in the end, but I still swear that the second cour was entirely filler (and joke that it should've been given to X'amd, which until now was considered E7's spiritual successor, since it needed more episodes) and it had a lot of situational gags which I know where supposed to be humorous but I just didn't find so. Eventually I'll rewatch the show for a full review, I meant to do that but didn't have the time last spring, but in the end while I still want to buy all of E7 I'm now torn on getting AO, maybe if I get it for a good price and just pretend that the ending is way different but usually when I say that I end up not buying the show, I'm just going to have to think about it some more. As it stands I give the show three our of five stars for having some really good bits but yeah, those last two episodes. :\
