TL;DR: This is shaping up to be the best arc in the series yet. Can't wait to see the next movie now. 9/10 Up until now, the Princess Principal arcs have all involved trying to help someone else, or trying to keep the Princess' secret from getting exposed. Which is all interesting and helps in world-building, but the girls have never felt in danger or been up against an opponent who truly tested their abilities. I won't spoil any more, but this is the first arc that truly feels like the girls are up against an opponent that is one step ahead and stronger than theyare, raising the stakes a lot higher. The series is feeling a lot more like a classic spy action movie now.

The setting, new characters, and music are excellent as always. If you liked the series or first movie, it's the same quality. It also has the best fight scene (both choreography-wise and animation-wise) in the series so far, and the girls are tested to their limits.

The only possible negative of note is that the ending is a cliffhanger ending, so we're going to have to wait another year or so for the next entry. I for one can't wait!