Finished the Yue Fei campaign on hard, here are my thoughts (Spoilers)
Hi! I finished the recent campaign on the hard difficulty, and it was overall a pretty good experience, and as a Chinese history fan (and Chinese) myself, here are my thoughts on the campaign. But TL;DR: Campaign good, presentation great, history good, gameplay good.
Presentation
What needs to be praised the most is the presentation of the campaign. The music, overall direction and cutscenes all received a pretty massive bump from the prior ones, being close to the prior games in narrative (Narrator talking about a historical period over a few slides of pictures). While I personally believe they could've done more with the dialogue in game; I also understand that AoE4 campaigns are considerably more serious and documentary-based than that of AoE2 and even AoE3. If I must pick one weakness, is that I would've preferred chinese pronunciation of the cities, however I recognize that this is a specific preference of mine. All in all, this is probably the best presentation so far! I will somewhat miss the old documentary-style presentation, but this type of narrative is how you get more folks interested in the history of the era.
History
In terms of presentation of the era, most of the important events in Yue Fei's life made some form of appearance. The portrayal of Qin Hui as a Jin inside agent is a little ahistorical, but his role in framing and killing Yue Fei has given him a reputation just as bad as a traitor. What is a very good nod to history is Qin Hui's response of "perhaps there is" to Han Shizhong's (Yue Fei's friend) question. This has been a proverb to mean "there doesn't need to be one", equivalent to an admission of fabricated charges. Extra credit should also be given to the showcase of Song naval prowess over the Jin, as the same naval prowess is what kept the Song Dynasty on borrowed time against the Mongols.
The Song-Jin Wars was just as bitter as the campaign has made it appear. However, it is important to note that Song had almost as many faults in the breakdown of the alliance. During and even after the conquest of Liao by both, there were many diplomatic and military incidents between the two. Of course, it does make sense from a Song perspective to not be fond of Jin at all. Overall, the history does do justice to the period, and it's a great introduction for anyone interested in (my personal favorite dynasty) Song historiography! For anyone interested in the rise of Song Dynasty, there is a Chinese TV show called "Swords into Plowshares" that is about the period before Song.
Gameplay
The gameplay is overall good, but I have a few gripes with it. But let's start with the positives! First of all, credit must be given to the way they exported Chinese faction into the campaign! The Dynastic system being the different phases of Song restoration and recovery in the aftermath of their loss in the North is fantastic. Yue Fei's involvement in the gameplay is great too: His death in battle does not result in a defeat, and he doesn't take the core gameplay of AoE4 hostage with his strength. What I particularly enjoyed is the diversity in the campaign's objectives. Every battle gives you a different victory condition to achieve initially, reducing the fatigue created by constant build-and-destroy macro missions. This is also not to mention the push and pull of being on the offensive, or defensive. You go on the aggression just as often as you're forced to defend a key objective, playing well into many different players preferences.
Most importantly, this campaign does a great showcase of the Chinese civilization in its strengths: That being their diverse army composition and versatility. ZGNs, Fire Lancers, Palace Guards, Nest of Bees, even Grenadiers all get a chance to show their worth in this campaign. Imperial Officials also gets a lot of mileage from supervising the barren gold deposits in a few maps, and rushing out important university techs! Even the more generic options like Knights and Crossbows gets a lot of chances to show their worth! I personally find slow push civs to usually be boring to play in campaigns, especially in favor of the more explosive knight play. But Yue Fei's legacy really showcases the strengths of the Chinese infantry and gunpowder, without neglecting their other options like Knights!
However, I do have a few problems with the campaign, and most of them are somewhat contradictory to the strengths I listed earlier. Even though most campaigns has had a pretty strong victory condition at the start, the second phases of most battles still ultimately come back to some form of search and destroy. This isn't too bad of an issue, as AoE4 is ultimately a RTS game with macro and build-and-destroy at its core. But being forced to destroy the 10th Jin keep gets a little repetitive at times. And on a similar note of contradiction to my earlier points: The Song Dynasty misses out on a lot of other core strengths the Chinese civilization also has. Eruptors are very fun and interesting as an unit, yes, but we're also missing out on Pyrotechnics-boosted, Spirit Way boosted Hand Cannoneers. We also do not get access to Bombard with reload drills, and are forced into trebuchets for most of the campaign for sieging. This may come off as picky, of course, but I personally believe that the civs should be as close to their MP counterparts as possible, to better ease SP folks into MP. These two smaller points being my main gripes should also tell you how highly I found the gameplay to be. Lastly, on a gameplay side of things, I also just found the campaign to be a little too easy, even on the hardest difficulty. For reference, the only mission I had to restart was the night raid, and that was largely due to an improper understanding of the objective (did clearing the Jin defenders include the buildings?)
On a more technical level, the sound design for objectives became exceedingly irritating very quickly. There were at least three missions that had an enemy spawn in attack waves, heralded by a horn sound effect. If many of these waves activated at once, your eardrums would quickly be overwhelmed by the sound effect. The spawn in for some of these waves often happens out of nowhere too, giving me a really nasty surprise when besieging Jin forts. A lot of the objectives and rewards also don't get explained very well. For example, after taking the first city in Xiangyang 1134, you are still restricted to feudal age, without being told how to reach castle age. The rewards for some of the side objectives are also really poor, such as in defense of Jiankang where you are tasked to rescue allied units, but you often lose just as many units in saving them. I feel like a slight buff would really help with these cases.
Conclusion
I think the campaign is pretty good but maybe wait for a sale if you're a campaign-only gamer. I found it to be a massive improvement over the older campaigns, and I'm eager to see what the next campaign will be!