Endings are important to me, when the writer completely gives up common sense in the final episode flipping the proverbial table, then I tend to just lose it & from then on I won't be able to write an objectively fair review.
Twenty-Five Twenty-One's ending made me change my rating from 9+ to 3.5. Trying to look at this objectively I think Who Rules the World's ending is even worse, perhaps the worse ending I have ever reached. The only reason I'm not THAT harsh in my scoring today is because at least the romance has not been ruined, but everything else is, what happens in the final episode is so egregious that I can not easily put it into words.

I'm so angry that I'm really not in the mood to talk about the good things. Just to sum it up real quick, the romance is really really good in this one, which is about 40% of the drama. Chemistry, bickering, cuteness, fluff etc it's all there, it's as good as it gets from a semi-historical show. The palace politics genre is something I generally hate watching, but in this drama up to maybe episode 25-ish it was really really well done. (there is only one evil queen, so the usual cold palace concubine garbage is mostly not there) At that point I still thought a 10/10 final score would be possible. In the later half though the plot deteriorated quite a bit, however after watching episode 38 I thought this would still be at least a 8/10, but then the ending came..

The Wuxia part of the drama is good and bad at the same time. There are many Relatively well done fight scenes & we go through various Wuxia classics, it even has a saint's trial. However the whole thing in the later episodes about armies clashing & whatever else is pointless to me.
In an acceptable Wuxia-world (no pun intended) strong cultivators decide the outcome of all battles & a weak king without the permanent support of a strong cultivator can never amount to anything ever, no matter how big his army is. Since if he offends a cultivator, they can literally just enter the palace & kill him effortlessly. I think the argument that this is not the case in this specific fantasy world is a bad one, since something similar happened not once, but twice in this show.
Also there were two plots related to cultivation that I thought were incredibly bad. The first one is about the theft of that certain technique, that's something absolutely insane, so much so that no self respecting wuxia writer would ever write that, because it's like fan fiction. The other one is the potion that supposedly disperses all inner force, though my dislike of that is more of a personal preference, it's not completely unreasonable.
Oh I almost forgot FL's sect is supposed to be one of the top righteous sects in Jianghu, however they are repeatedly the useless pig teammate throughout the entire show (useless+weak+stupid the whole lot).

If by some random chance someone who has not watched this drama yet chanced upon this review, my suggestion to you fellow MDLer is to maybe watch up to episode 38 & then just pretend the show only has 38 episodes & call it a day. The romance gets proper closure by that point-ish.