To start with the characterisations of the leading trio are well done.
Pacifica, the titular Scrapped Princess, is consistently coming across as "nice kid, not too bright", enough so for both my housemate and I to make the observation simultaneously on a couple of occasions.
However, this does generate a fair bit of sympathy. Pacifica may not fully understand her situation , but is definitely trying to do the right thing.
However the standout character is her elder sister and Guardian: Raquel.
Raquel is a thoroughly competent (and more than a little scary) sorcerer who tends to present a Yamato Nadeshiko front to the world. Raquel is one of, if not the, best sorcerers around.
This caused a amusing moment in a recent episode when she described herself as "one of the ordinary ones". Cue housemate and I going "In what sense are you ordinary!?" (or words to that effect). 
Raquel is so consistently presented, and so beautifully voiced by Sayaka Ohara, that the character is always a joy to watch.
Shannon, Pacifica's elder brother and Guardian, is also nicely cast in the swordsman role, as well as the protective elder brother. He completes the trio nicely, and the family dynamic is well handled throughout the series.
Another interesting element is the worldbuilding: for a relatively lightweight series there are some nice subtleties here, and they are carrying the story well.
 Which is understandable. It is actually harder to believe the ease of understanding some of the other characters have.
 And doing so simultaneously as well. :)