Like too many medium-length mecha series these days, it starts off (too) slow, picks up a lot of value half way for the better, but runs out of steam too early. *sigh* Production I.G could've done so much more.
It's got a bad beginning and an unsatisfying end. For the most part though, if you can make it through the first few episodes it's a great mecha series. It's got little to nothing in common with the original Reideen and its other remakes.