I'm not sure if it's a hidden gem, but it's definitely a gem and a 10/10 in everything.

#1 It has gorgeous cinematography. They really put thought into directing and what would be best angles and scenery. Simply pure beauty to watch.
2# The writing & plot was excellent. Not a thing too much or too little & thoroughly riveting. Each character had a role to play. If I didn't have to go to work next day, would've binge watched it all in one go - it's that good. Keeps you on your toes and excited for what will happen next.
#3 The music:
1. The opening title itself already has lovely music & the animation also is great.
2. The drama had few notable pieces throughout the drama but they were truly captivating and used perfectly for each scene that it had your complete attention and only heightened the emotions to the very top.
#4 They picked the right actors, that's for sure and boy did they deliver. Top notch acting & performance.

And miscellaneous #5:
1. The overall pace...while exciting, I'd say was rather measured and calm, yet kept you on your toes.
2. The good, the bad, the morals? The drama was, I'd even say, a good moral portrayal of human nature & society - there is no white or black - it's all gray. One can not always choose what to do, the situation may push you into it, or in fact, it may mold you to be what is needed even if afterwards you get cursed for it.
3. The many varied relationships & their changes.
Honestly, the drama had such excellent interactions & exchanges between the characters and how it changes & develops with the story... it's so good to watch.
I'm not gonna go into spoilers, but once you're halfway into the drama, you'll realise that our female lead & a certain minister have excellent chemistry - be it between the characters or the actors, and I don't mean it in a romantic way, but the two of them together make you wanna go - yasss, burn them all, if those two are together, nothing can stop them.

And a special mention deserves our female lead. Sadly, rarely do we get such excellently written female leads. That's who women are and can be. You think you control her, yet in the end she's the one to control you.
A true queen indeed.

Bloody Heart is a rare excellent & riveting drama that does not often come by. A must watch for sure.

And I didn't even mentioned romance, because while it is there & actually plays a rather huge part...everything else is so amazing that it actually kind of overshadows the romance if you start to think about it. The cinematography, the plot, the characters & their relationships...that takes precedence. Because it's simply that great.