It's a great show, in my opinion.
I watched it believing it was going to be some sort of "lighter and fuzzier" knockoff. This, fortunately, turned out not to be the case. The first two episodes were a cosmic mindscrew, but by episode three it became quite watchable. It takes the show some time to mature into its own, but by a good six or seven episodes in, it begins owing less and less to Eva.
On one hand, the characters are slow to develop, but, on the other, they are well-thought-out, many-faceted pieces of work. Such depth is rarely seen in mech anime, and it sets Rah apart as being a cut above. Even the villains and meaner TERRA
leaders get their day in the sun.
There are scenes of institutionalized child abuse, both physical and emotional, in episode 15. (I think it's 15.) This is where I have to criticize it the most: It's extremely hard to watch, even if you have a strong stomach like me. It does, however, serve to add a tinge of tragedy to the backstory of one of the more unlikable characters.
The soundtrack is as good as it's chalked up to be, the animation is beautiful, (I don't like how the characters are drawn when they're in profile, but other than that, it's great,) and the story is compelling. In short, I would recommend RahXephon
I really have to withhold judgement as to whether it's better than Evangelion, though. It's certainly far, far more accessible, and the budget is clearly several times Gainax's budget for Eva. And the main character isn't as whiny.