This episode was very interesting and informative. I really enjoyed watching it. For a few episodes before this one, the battle against the "floating stars" had been dragged out, but in this ep, the action really began.
It was also a dramatic episode. Along with Zofis's ways of manipulating the Mamodo, Zatch being "naive" was questioned by the opponent. That definitely perked my interest level up a notch.
Anyway, if you plan on getting the main plot of the show, this episode is a must-see. It includes a lot of information (especially in the flashbacks) that is needed to understand what is going on in the show.
Overall, an awesome ep. Definitely worth watching.