Pretty disappointing series which really started to annoy me towards the end. Although some of the concepts were quite nice (singing mechas! Heh!), the story behind it stood on very wobbly ground, with a lot of plot-points which didn't make any sense or had no relevance at all. If there's anyone out there who could explain to me why the Mu put Tokyo into a timebubble in the first place, I would be very happy. The only use I could find in it, was that they would have a plot-device to create the Haruka/Ajato-Storyline. Apart from that it was very unclear to me what the Mu were trying to achieve ("We want to tune the world!" doesn't say anything to me) or what their whole war with TERRA was actually about. And why exactly were they a threat to humanity and how did TERRA know? Information that was simply missing.
Then there were quite a lot of subplots which sat there totally independent of the main-story. Most of them felt pretty useless in retrospective (especially the two Megumi-Lovestories) and made the impression that they were just there so that they had enough material to fill 26 episodes. And... keyword "lovestories"... there were too many going on at the same time. Especially in the last few episodes it started to become really ridiculous when there were about 5 or 6 women (maybe even more) in love with Ajato at the same time or had at least a crush on him.
A lot of people made a comment about how rich and well fleshed out the characters are. Well, my impression was the exact opposite. Almost everyone in the series seemed very flat and uninteresting to me. And yep, underdeveloped. Maybe it's because they had just too much characters on board, so that it was too hard to focus on everyone. But when I take at the "X"-TV-series where they had a LOT more characters to work with and yet they were all more than your usual stereotype... and considering that they had fewer episodes to offer... Hm.
Even some of the main-characters had their flaws, especially Ajato, whose characterization seemed to flip around from now and then and suffered from inexplicable mood-swings. When it was necessary for the main-story Ajato was an angry, impulsive guy. But then he could be very understanding and calm although the situation was (still) the same. And these irritating mood-swings could happen within minutes. VERY inconsistent writing, in my opinion...
The other thing I was wondering about was why so many people are persistently proclaiming that this is NOT a copy of "Evangelion"... and how much it stands on its own feet and how much more it is different from the GAINAX-series. Well, hum... Apart from the very similar character-designs (watch out for the twins of Misato, Asuka, Commander Ikari and Ritsukos brother) and yep, even set-designs (hello, pyramid!), "RahXephon" copies entire episodes from its predecessor. Here we have the "hero gets unconscious in the mecha and has surreal dreams"-ep, there is the "evil mecha who sucks his enemy into another dimension"-ep, and so on... The same goes for some of the plot-lines, like the one about the old guy who pulls all the strings in the background to achieve his own personal goals (he even has a German name - like in "Evangelion"). But the most obvious rip-off of them all can be witnessed in the last two episodes when everything goes "End of Evangelion", but in a very stale, shallow and meaningless way, lacking the philosophy and the depth which made the EVA-series and -films great. And when most of the questions are left being unanswered it doesn't feel mysterious or exciting in any way. They're just gaps which result from bad editing and even worse scriptwriting.
The only good positive aspects were the great animation and the decent soundtrack (lovely title-song). But that alone doesn't make a good show.
All in all an anime-series which wants to be important and meaningful at all costs but actually doesn't have anything to say. Underneath the pseudo-complicated plots and the pseudo-intellectual psycho-babble there is nothing more than hot air and a lot of steam. Very disappointing and not worth a second watch.