RSMasterfade

In term of attention paid to the historical setting, this show is head and shoulders above Minglan. In many respects Minglan's portrayal of Song was the exact opposite to the real history. Take one of the most glaring misrepresentation - slavery. Chattel slavery, legal and widely practiced in Tang, was completely abolished in Song. All house servants were free men and free women working under contract, so if anyone were to beat their servants to death, they would be put on trial for murder. Chattel slavery was reintroduced to China after the Mongol conquest. The first Ming emperor tried again at abolition but didn't succeed. So some key (and heartbreaking) moments in the show could have happened in any historical period but Song.

Also, the show had the Sheng father and son serving together in the capital, which was just impossible in history. Song had strict anti-nepotism laws, to have son and father both serving in the capital required special wavier from the emperor which was almost never granted - the Censorate would have a field day if an emperor tried, so it's reserved for the emperor's favorites and even then only under exceptional circumstances. Qi Heng and his second father-in-law were also both serving at court in the capital - impossible for the same reason.

The show also portrayed the Song upper class as obsessed with birth and noble titles, which was again opposite to what was true. Song marked the fall of the power of the Chinese aristocracy. All important government positions were available only to people who passed the exam and everyone wanted to marry their daughters to top rankers regardless of birth. Minglan's story would make a lot more sense in Tang, when the aristocracy was so powerful the most prestigious aristocratic families would refuse to let their sons marrying princesses because they considered the imperial family beneath them. The original novel behind Minglan had no historical period attached, and the script writers (or the investors, who knows) decided to make it Song. It's not just a poor choice, it's the poorest choice possible.

The costume design in Minglan were also overall inaccurate. The formal dresses for ladies with conferred titles were good. The minister's court dresses were fine but the emperor's court dress was atrocious. GTY's wedding attire was wrong - people wore formal dress to their wedding, commoners didn't have formal dresses so they were allowed to wear an official's semi-formal dress, GTY was a high ranking official so he should have worn his formal court robes with the corresponding hat. A groom going to his wedding without a hat was just unthinkable, far more unthinkable than going to a black-tie wedding now in evening dress and Crocs. The casual dresses in the show were generally bad.

Sorry for this wall of text. I have long felt that the Story of Minglan presented a very distorted picture of the Song society, but people believed it because it was presented with such earnestness. So I have to let this out.

(Minglan's director's next show is also set in Song, but the original novel it based was well-researched and the the trailer looked much better than Minglan in terms of historical details. I'm a fan of the original novel, and I'm very much looking forward to the show. )

On the other hand, the Longest Day in Chang'an is the really deal. It's not 100% correct (for example, people have pointed out that Penzai in the show used Song era pots/planters rather than Tang era ones), but it's better than anything that came before in term of period details. It's attracting attention not just in the popular press but also in the more rarefied circles of universities and museums, and not just in China. I just saw a tweet from the associate director of the Eisei Bunko Museum in Tokyo commenting on the show's excellent set design.

Viki volunteers are not paid, but in the case of the Longest Day in Chang'an, the subtitles were provided by the Chinese rights holders. This has been confirmed by the Viki Channel Manager on the show's Viki comments page. The same subtitles appear on Amazon and YouTube.
Unless the Chinese rights holders asked one of their managers' second cousin who happened to study for TOEFL in an American college to do the subtitling, they probably paid their translators, and they're not receiving a proper service.

It appears the second season has completed the censorship process. Youku just changed the episode count to 48 and updated the release schedule to 6 episodes a week.

Many of the most glaring errors in the subs were made on relatively simple sentences.

Consider the lines @ 4:20 into the first episode:
Chinese: "这是望楼。今日于你有大用。“
Word-by-word translation: "This is watchtower. Today to you have great use."
Subs:"This is the watchtower. We have use of you today."
Correct translation: "This is a watchtower. They'll be of great use to you today."

1) Chinese doesn't have articles, so the translator must assess the context and decide whether to use definite or indefinite articles. Since there were many watchtowers in Chang'an and there's no reason for Tan Qi to single out a specific one, the correct translation should use the indefinite article. This is Chinese-English Translation 101.

2) Chinese, like English, is a SVO (subject-verb-object) language. The second sentence omits the subject. The natural assumption is it continues to use the subject from the preceding sentence, and in this case the assumption works out well. On the other hand, the subs introduced a new subject ('we') out of nowhere, reversed the subject and object in the original sentence, and produced a sentence that made no sense in the context (why would Tan Qi introduce the watchtowers in the first sentence and then immediately talk about something completely unrelated?).

Both mistakes were very basic, and remember we're talking about professional translators who're getting paid for their work. This is just unacceptable.

PM me if you do get in the VIKI subs team. I can compile a list of serious translation (not stylistic) errors.

The sad thing is that the subs on Viki, Amazon and YouTube are done by the production company, so one must assume that the subbers are professionals getting paid for their work. This is yet another example of the lack of professionalism in a lot of Chinese businesses nowadays. I re-watched ep7 on Viki last night, it seemed to me that multiple times during the episode the translator(s) just gave up trying to understand the original Chinese and made up sentences to fill in the space. Just scandalous.
If you want to volunteer for Viki I think the way to proceed is to PM the channel manager.

For a YouTube channel charging 4.99 USD/month for a single show, one would expect some QC on the English subs, but sadly judging from the first free episode it's in the same sorry state as the subs on Viki and Amazon. Unlike Viki and Amazon, YouTube does have Chinese subs, so it works for Chinese speakers who needs subs to understand the more difficult dialogues (the YouTube channel is currently the only legal way in the U.S. to access the Chinese subs). For everyone else my advice is to stick to Viki and hope other users will point out serious mistranslations in the comments.

PSA: in the U.S. at least, this show is also carried by Amazon Prime & they're a few episodes ahead of Viki.

For anyone who's finished the first three episodes, I highly recommend endlessthoughtsofafangirl's guide on Tumblr:
(Do be warned: most characters in this show are based off historical figures, if you know Chinese history of that period you'll already know who's going to survive this story. If you don't want to have that knowledge don't read this)
https://endlessthoughtsofafangirl.tumblr.com/post/186029840425/a-guide-to-the-longest-day-in-changan-%E9%95%BF%E5%AE%89%E5%8D%81%E4%BA%8C%E6%97%B6%E8%BE%B0

Since you mentioned lighting, here's a tidbit: a lot of day scenes in this show were actually filmed at night with artificial lighting, because the director insisted the angle of the shadows must match the time of the day, thus made it impossible to film all day scenes in daylight within a reasonable schedule.

There are romantic subplots, but they're not the focus. Think Nirvana in Fire.