(This will be spoiler free, and as a result, brief. I don't want to give away a thing!)
I recently finished watching this series and I have to say that it has been one of the best viewing experiences of my life.
The animation is fluid, smooth, and breathtaking. Strategic placement of various backdrops and images enhance the story, whether by foreshadowing an event to come, or connecting an event from the past.
You can tell from the titles themselves that RahXephon has a very strong musical undertone, and in fact is an integral part of the story. The result is music that is haunting, stirring...memorable.
Above all else the characters are what makes or breaks a story - and these made it many times over. The diversity of characters ensures that you can relate and empathize with at least one, if not more. They are simple, complex, mysterious, or a little bit of each - tied together with the perfect voices, making these characters come to life. You find yourself laughing with them, crying in sorrow, in rage, in joy. You no longer see 'characters', but real souls going through myriad experiences and taking you along for the ride.
After finishing this story I find myself feeling as if I had lost a close friend, since I will never again be able to discover this world and these people for the 'first time'. I'm sure all of you have gone through a similar experience, and realized how profound it was, and how much you wanted to share it with your family and friends, anyone who would listen. RahXephon has been such an experience for me, and it is one I will not soon forget.