I loved Longest Day in Chang'An (though not a perfect drama) so I was excited for Luoyang, since the screenwriter was the same. Unfortunately, the things I didn't like about Chang'An were multiplied and increased in Luoyang, which is to say: unevenly developed characters, poorly constructed character relationships (specifically M/F relationships), unnecessarily 'twisty' plot twists and an unsatisfying ending.
I kept watching mostly because Huang Xuan was such a compelling actor - this was my first time seeing him - but all the other mains were flat and boring. Though I don't blame them entirely, it was partially a script problem - I never thought any character would fail the Bechdel test as badly as Song Yi's character did. Both M/F relationships had no chemistry and seemed to add little to the plot.
Good parts were the cinematography (though not as good as Chang'an), Huang Xuan, and a few of the minor characters.