First to find this drama, I found the ML is not too attracting, but once he slip to Tang dynasty and change his hairstyle, I found him charming enough to be ML. What is more important is I didn't found FL is annoying at all.
I enjoy the story until episode 16 when situation drastically changed.
However it's not getting too bad and I am able to find the storyline is reasonable. Except you turn hating Crown prince, nothing really damage the story.
I wont spoiler the ending here, I hope you can grab it since it's worth to watch!