Let me start with the opinion of the top Hollywood critic Justin Lowe, who writes of director Hwang Dong-hyuk’s effort:-
Hwang competently orchestrates the film’s disparate political and strategic developments, but there’s little sense of stylistic inspiration or narrative innovation — it’s all pretty conventional.
It is a typical self-contradictory statement. For if director Hwang Dong-hyuk orchestrates competently the disparate elements, what does it matter if it is “pretty conventional”? It would matter if it were “ugly conventional” as hundreds of films, especially Korean ones, are and receive prestigious awards they don’t deserve. This critic does not find “a sense of stylistic inspiration”. But what does he really mean and what does he compare it with? He does not say. But he does say –
Hwang’s handsomely mounted production benefits from authentic historic locations and top-notch production and costume design, along with a stirring score by Japanese composer Ryuichi Sakamoto (The Revenant).
Most comment mention the music of Inarritu’s The Revenant (2015) but do not dare say that The Fortress has just as good cinematography and deals with much more important issues than vengeance as in The Revenant which received so much (deserved) accolade.
Surely it takes a very good director to bring together all the elements mentioned by JL (and more). In The Fortress we see angles and vistas of excellent photography. I was reminded of David Lean’s 1962 epic biography of Lawrence of Arabia except that here we had endless stretches of snow instead of Lean’s desert sand, scorched in sun and heat, and Chinese and rugged Korean fighters instead of Arabs, who had just begun to feel their nationality. Or one might compare it with Kevin Costner’s 1990 epic Dancing with Wolves and its expanses of meadows of desert or fertile land and Indians and buffalos in bright sunlight.
Here is the expanse of snow and frost….

Here is the invading, galloping riders:

Here are the arrays of soldiers waiting in the beginning:

Lowe makes another misdirected comment regarding the arguing of ministers whether to fight on against the odds and retain dignity and honor (Kim’s line) or surrender but ensure survival (Choi’s line) – plus a possible hidden theme of rehabilitating Choi as national hero, not a traitor:
Students of Korean royal history might find these intricately courtly exchanges of particular interest, but for many others they may produce a mind-numbing effect. Nearly an hour passes before the fortress’ soldiers see any action at all, and the sole set-piece battle is too brief altogether as the Korean forces beat a hasty retreat from the overwhelming Qing army.
True, some may feel mind-numbed by these scenes, or angry or dismissive. But any patient viewer will notice a lost tradition of dignified and respectful order within a seemingly authoritarian regime. Today we have neither dignity nor respect – nor, of course, the slightest intent to sacrifice our life, as these, to us, so custom-bound, superseded men.
On the other hand, the film shows quite explicitly the strong class bias of those aristocrats (well-exemplified by the prime-minister who was also the -incompetent – Supreme Commander) against the peasants and manual laborers and all lower-class people. It comes out clearly also with the poor orphan girl, whom minister Kim nurtures and during the merciless bombing protects with his own body, and with the blacksmith who delivers Kim’s message to the waiting southern army but is ignored and almost murdered by the cowardly officers of “nobility”!
Lowe makes a rather silly error in saying that “nearly an hour passes before the fortress’ soldiers see action at all”. In fact, they see action at precisely 29.30 minutes and in that battle emerge victorious! A mere slip, perhaps.
Lowe misses two more important points.

a) The little girl, granddaughter of the old fisherman whom Kim himself slays so that he won’t guide the invaders through the secret passage to the fortress. Surely, she is, even if unbeknown to the director, the soul or spirit of Joseon which survives thanks to the honourable and dignified aristocrats exemplified by minister Kim. The peasants were the backbone of the nation. And in the end, she is entrusted to the blacksmith, also low class but handling the technology which promotes any nation’s progress in the world. She assures Kim that when spring comes, the dandelions will blossom again, and she will herself catch a perch in the unfrozen stream and cook it for him!
To stay with the arguments of the ministers, one side for life and survival (minister Choi who, wrongly, was thought to be treasonous) and the other for dignity, honour and national tradition (serious Kim) is to stay with the obvious.
The script and photography point to subtler, finer values.
b) The acting which is superb in its expressive sobriety and economy.
Lee Byung-hun as Choe Myung-kil (left in picture), the advocate for surrender and survival is in probably his best role.
Kim Yoon-seok as Kim Sang-hun (right), the conservative, loyal, intelligent minister advocates honour and fight and is probably the best actor of them all.
Park Hae-il as king Injo (center below) expresses well his inner conflict and humiliation finally as he submits to the Khan.
Gho Soo too is excellent as the back-smith, embodying intelligence, courage in battle and tenacity for survival (to the right of the king).
Park Hee-soon is also excellent as the commander of the fortress soldiers (to the left of the king).

Considering all these aspects, one cannot but vote this movie as probably one of the best Korean efforts in cinematography and perhaps one of the best in the world. It shows clearly that director Hwang has left far behind the uncertainties and exaggerations in the 2011 Silenced (winning Best Film awards in 2012). And it should take its rightful place instead of the absurdities the new Korean cinema (Squid game, The Parasyte) so abundantly produces.
It certainly deserved all the awards it won in 2017 and subsequently.