I will not go over the plot as other viewers have already done so. Instead, i will focus on:

Acting (main leads): Superior acting by both ZYW and ZQY - they are able to capture the little nuances of emotion - anger, pain, love, consideration, etc
The ML (Lord YuZhang/Xiao Qi) - No, he’s not handsome by any means but what Masculinity - he’s gentle, kind and treats the FL with respect: protects her. He’s always patient with her and doesn’t interrupt when she’s speaking. While the male protagonists in C-dramas are supposed to protect their women, few are so gentle and treat their women so gently. Yet, he’s strong on the battlefield and doesn’t hesitate when he has to fight/protect his country/his soldiers and the people he cares about.
He’s got a new fan.

Roughly translated. I am not a translator by any means, so please excuse me if I got this wrong.

Wang Xuan asks: So many people have changed. Will you also change?
Xiao Qi: To you, I will definitely not change

Oh, we should all be so lucky …
The FL (A-Wu/Wang Xuan) - Many reviewers have leveled criticism that she’s too old to play 16. Yes, that is true but FL has the gravitas to convey different levels of emotion with her eyes, her face, her body movements - many other actors do not have this depth of skill. So, in the beginning (first 8 episodes or so), the disparity threw me for a loop but I got over as the drama continued.
Both are in an elite group of actors that are able to make the viewer feel for them, feel their happiness, feel their pain, feel their anguish. I must admit that not many actors have been able to do that me but in Rebel Princess, I feel what they are feeling.
Lots of characters die in the end, but I’m glad they lived on as commoners, with their children. This is an ending that I particularly liked.
(Other actors):
Gen Song (Lord YuZhang’s right hand) On his wedding day, he looks at A-Wu instead of Yu Xiu;
He changes from a good person to one who is greedy, wants power and covets A-Wu. Alas, he does not get a good ending. His wife (Yu Xiu) dies to protect him from rebelling … in vain though
Yu Xiu, ZiDan (sorry excuse for a man- he’s supposed to know A-Wu well yet he insists on just saving her from danger without realizing that she will not escape and leave the rest of the people to die): All did a good job and added to the drama as a whole. It’s rare in C-dramas that almost all the cast have strong acting skills.
OST: Beautiful and Emotive, especially the song at the end of every episode. When I listen to that song, there’s a longing, a melancholy and their love.
Costume + sets: Well done with much attention made to the details. Beautiful costumes.
Final Thoughts:
A few parts of the plot are not explained but that’s to be expected. Also, I felt that the last 4 episodes sort of rushed the ending. Still I would watch it again. This is a masterpiece that is hard to beat.