Update: The plot really does not improve, so just spend time on this drama to enjoy the looks (not the acting) of the leads and supports.
I also wanted to share how much of the background music is recycled from Royal Nirvana--where the music was amazingly in synch to the story and scenes but just seems to amplify angst in this drama. But that said, this music has also been used in Allen Ren/Bai Lu's One and Only as well as Ryan Ding/Yang Chao Yue Love You Seven Times, and even in Love and Fairy and Devil (which is even rather interesting, as Li Yi Tong who starred in RN is also in this drama) ---so perhaps the music is not even original to Royal Nirvana..

So as to the plot....

The first handful of episodes are 'fun' as Dilraba plays a smart and flirty girl, so you may overlook how lame the plot is to make her look intelligent and then it goes downhill dragging out the angst and guilt and obsessive greed to gain at the expense of the good of the people. The greed plots are lame-best example, the fake FL wants to become crown princess at all costs--but nobody points out to her that she would be choosing to escape one perceived imprisonment to another as a royal behind the palace walls--and of all people, the Crown Prince insists on her selection while insisting the girl he does love isn't chosen because he doesn't want her stuck being his wife.. So huh? he's insisting the fake becomes his wife simply because of a promise even if he knows it will make that person miserable--and he's the hero?
Those around the fake can bring armies to the fore but choose to be powerless to stop her and yet feel guilty that she was in a gilded cage...after barely being to eat when she was found...you could argue she was not given a choice when she became the fake-but still, isn't being housed, safe, elegantly clothed and educated a bit better than struggling to survive? And she insists on more than that to become a princess at the obvious risk of deceiving the emperor and losing her life? Is she really that dumb and yet conniving enough to pursue her obsession?

The story does not improve--the plot/script last arc of episodes are ridiculous---I have to point out my observations:
--They go to war...but as soon as FL is in supposedly in trouble, the ML drops everything to 'rescue' her--but whereas he isn't busted for doing so, the SML is-for defying imperial orders....but then when things end up badly...they seem to just hang around until FL decides to take action. and then suddenly there's an urgency to act--wouldn't they have been strategizing a response from the get go? And why is it she can just go to war with no provisions/resources?
--ML ends up being cared for by enemy princess...and it's just all good...um? where did she have the resources to save him? why save him? why isn't her brother figuring out the ML is there?
and I could go on, but others have already so will stop here.