The most unforgettable dramas are usually stories that often portray characters stuck in a backdrop of conflict, holding onto their innermost moral values against all odds and temptation whilst they experience challenges and setbacks. Nirvana in Fire is a thrilling watch because the main story, which revolves around the Lead Hero (Mei Chang Su) and his desire to redress the injustice committed against his father (a decorated Imperial military general) and the Chiyan Army battalion (led by him and his father), weaves multiple plots involving many other characters trapped in an unavoidable web of power and politics.
Hence, the title of this drama is rather apt- Mei Chang Su's "nirvana" is his own idea of perfect justice and this drama is literally his quest "on fire" to reclaim his past injustice.
As this is my first time writing a review for a Chinese Drama, I won't be commenting on music score, cinematography and acting skills. Here's my take on the Story, after watching 54 episodes of NIF:

The Villain is not who you'd expect (SPOILER ALERT)
Every drama has a big bad villain whose job is to throw countless obstacles in the path of the Protagonist and NIF is full of them. The drama almost had me fooled when it led me into thinking that the bad guys were Xie Yu, Prince Yu, Xia Jiang or Ban Rou. The biggest villain is only hinted at the start and only confirmed right at the end when you realise the culprit behind all the fights, wars and killings is actually the selfish cowardly Emperor, who had the heart to allow the murder of his own son, a capable brother in law and nephew, 70,000 of his own loyal soldiers based on 1 piece of fake information manufactured by a rogue informant. It is so damning to realise that the biggest culprit behind the shedding of innocent blood is the very man that all these characters pledge their loyalty to. Indeed, the most powerful man is also the most insecure person. The Emperor had been too quick to jump to conclusions about his own son Prince Qi teaming up with the formidable Chiyan Army to rebel against him, without doing any due diligence or fact checking, purely because he was super paranoid about losing his control and power and it was just too easy to act on his presumptions and instincts. The Emperor gives us a believable portrayal how "evil" people are just extremely selfish people who manipulate every advantage to gain more wealth, fame or power. And the impact and brevity of the past sins he that condoned and covered up for his own self-preservation, only really struck me at the end after I completed the last episode. The drama left me feeling anguished and thinking...why do people pledge their lives for this guy??

The Lead Hero is a quasi-Villain
Mei Chang Su as the lead character in this story of finding justice and redemption, is no doubt a shrewd strategist, but he isn’t a human without imperfections. In seeking to put his best friend Prince Jing into the position of ultimate power (to be the main contender for the Imperial throne) to redress the injustice committed against his father and the Chiyan Army 12 years ago, he meticulously sets out his plans by planting various people and rumours in various places. The way Mei Chang su’s pre-planned schemes unfold are only gradually and subtly revealed across the episodes, that you might even miss these clues if you don't pay close attention to the drama’s dialogue and script. There's a classic scene in an episode where Mei Chang Su bitterly remarks to Fei Liu (his young and impressionable loyal guard) that "it gets harder to feel any pain when the heart gets harder and hardened" after one of his pre-planned schemes exposes a buried sin of the father of his good friend, Jingrui, and irreversibly implicates their entire family. Despite the hurt caused to people around him by the gradual unravelling of uncomfortable revelations, he remains cool calm and focused on his goal. One can't help but feel sad yet admire our Lead Hero for holding it all in while he executes his mission with stealth and laser focus, knowing that even with a future reclaimed by Prince Jing's ascension to the throne, his incurable terminal illness (by the Bitter Flame poison) would ultimately deprive him of any foreseeable future with his childhood love, the brave and beautiful military general- Princess Nihuang. If Mei Chang Su is the biggest manipulator of the chess game, you could also say he is biggest tragedy despite his winning schemes and victories. Because our hero does eventually achieve his own happy ending, but he exits the world without the company of loyal friends and workers who stood by and dearly loved him. Well done to the script-writers. They wrote a really unforgettable character in the morally ambiguous grey hero-or-villain Mei Chang Su.

The 2nd Lead is the secret Hero
I’m really drawn to Prince Jing, the oblivious underdog of this drama, as like Mei Chang Su, he has also experienced the tragedy of losing his loved ones during the Chiyan Army massacre. If it isn't obvious enough, I think Prince Jing always appears cold, aloof and anguished-looking for a reason. He has to wrestle with the memory of knowing that his closest sibling and best friend were framed and murdered in a scheme that was commissioned by his own father and even as a Prince (albeit second rank), he is unable to do anything about it because he knows that as long as his egotistical cowardly father remains Emperor, no King will ever admit such a catastrophic mistake of this magnitude in public. Hence, he starts out being the “loser” in the story, not the first in line for the throne and completely ignored by his Father and looked over by everyone in the Palace. Prince Jing eventually gets persuaded by his elusive advisor, Mei Chang Su, to swallow that stubborn pride and personal dislike for politics in order to make himself eligible enough to be next in line for the throne, where being the future Emperor would grant him the opportunity to redress the misconceived betrayal of the Chiyan Army that led to the bloody massacre. Prince Jing is stubborn in temperament but also stubbornly loyal to people he loves that we constantly see him constantly getting irritated and inflamed with Mei Chang Su because he wants makes sure that no one innocent gets harmed or hurt in the process of Mei Chang Su's scheming. Because he cares so much about people around him and is entrenched by the hurtful memories of the past events, the Water-Brained Buffalo becomes so dense and oblivious to the uncanny similarities between Mei Chang Su and his best friend Lin Shu, that he eventually becomes the last one to uncover Mei Chang Su's real identity. I suspect the script-writers have intentionally built up the endearing bromance between Mei Chang Su and Prince Jing prior to this. So that when we see how Prince Jing realises that he can no longer be with his best friend (Lin Shu) after Mei Chang Su departs from the picture, we feel Prince Jing's pain and sadness like a double whammy.

So if I can sum up why I'd rewatch this drama again, it would be this: Intricate plot. Unforgettable Characters. Multiple clues subtly hidden throughout the episodes that makes watching this drama a stimulating but fun cluedo-hunt.
Watch and savour Nirvana in Fire. You're guaranteed to become a wiser and more introspective person after it.