I have never seen the original OVA, but from seeing the first season of this new one, its pretty good. Its short. And with most short series it has to wrap up the plot within its time allowed. The plot is pretty straight to the point for the 13 ep duration. Birdy has been sent to Earth to find Geega, Tsutomu who is exploring an abandoned building gets caught in the fight, his body severed in half. To save his life Birdy fuses with his consciousness and his body is sent to her planet to be restored. Together they must find the Ryunka, which ends up being figured out around ep 10. The last three eps are wrapped up in the last three eps quite quickly. But like I said, for being 13 eps its gotta get to the point pretty quick.
Overall, the story is simple, it has some good points, and I think it could be more then what was the end result. The animation is really crisp and smooth, the animation in the first ep caught my eye, and the designs for some characters as far as clothes were interesting. The op and end songs were good. I found this anime quite decent, and may pick up the boxset when it comes out. I have not seen the second season but will most likely pick it up. The series is different then some others and I really enjoyed it, if you want something that is eye catching as far as animation goes and simple entertainment, check this out.