There are many things that affects the ratings. Too long for me to make a list.

As a fan of sageuks and Korean history I'm happy that I finally get to see what I'd call a quality sageuk that fits my taste.
I just hope that NOKDU's reputation for quality will be weight over the ratings as not to discourage other production teams from making this kind of sageuks.
I get that it's expensive but it's so worth it.

Dramawiki always update ratings on the same day.

Personally, it's as good as Nokdu. It's the kind of sageuk where we can actually learn a thing or two because it closely based on real historical figures. Though I have to warn you that unlike Nokdu, Haechi's story mostly revolved around the palace politics and intrigues.

Hi @megane. In my opinion they are both excellent dramas. HAECHI had a fine cast. It was my first Jung Il-woo drama and he was impressive. For me the award for best performance by an actor in HAECHI has to go to character actor Lee Geung-young as Minister Min. He gave an awesome performance. I really enjoyed Go Ara’s performance until her role was affected by an accident on set.
As @gadis notes HAECHI is heavy on palace politics with a slew of characters to remember. You always will have something like that with a sageuk but for me what made watching the initial episodes a challenge was that the final 7 episodes of THE CROWNED CLOWN overlapped the beginning of HAECHI and I found it difficult watching both at the same time.
Bottom line I can recommend all three NF, HAECHI and TCC.

I haven’t watched Nokudo yet (all free time was spent on the outstanding Nirvana in Fire), but Haechi was excellent.

Accurate and if you can ignore the very obvious GOT swaggerjack.

Blasphemy! We are talking about an angel here.

Idols have really little effect on ratings. They only peddle online comments.

Shin Hye-sun has been a ratings driver since My Golden Life. The k tv viewers love her.

I hate the way idols - or the currently super hot actor - hype up the ratings of mediocre and downright bad dramas. It just encourages more bad dramas. I’m not familiar with anyone in ALM, but after 2 episodes, I dumped it. It’s a silly story that’s been done - and done much better - many, many times. Feels like one of those awful Hallmark romance specials. No thanks.

That is what I am thinking. Historically, idol dramas don't pull the high ratings even though they have a strong fan base, but they were diligent in casting the female lead and it followed a hugely popular drama.