A story that takes itself seriously.
Reading this sort of reminds me of the way US movies/dramas often portray the end of the world. As the author has bluntly stated in the synopsis - this is an apocalypse with no rebirth, no transmigration, no system - the sole focus is humanity fighting hard for their survival.
Here, humanity actually comes together to defeat a common villain: the aliens. Many touching topics are brought up: friendship, comradery, sacrifice. The political system hasn't entirely crumbled, likely because the cause of the apocalypse is aliens, not zombies. The government and the military remain an important role in coordination, battles and leading their citizens. Meanwhile, the Internet and many relevant institutes are still working fully to help humanity combat this unknown terror.
The leveling-up system is quite interesting as well. The characters' abilities need to be trained in battle, which could eventually manifest into many different forms. The logical thing here is that no one just suddenly know how to use their abilities, so every ability user needs to experiment and finds out for themselves how they can utilize their ability in the best way, be it for combat or for supporting the redevelopment of society.
The battles are very dramatic, I would say. Do expect that quite a lot of people will die along the process. The author is clearly strong at writing battle scenes, and I think that is one of the best things about this novel.
Now, on the characters. ML may be your staple OP fighter coming from a military background, but rest assured that he's no cookie cutter ML, especially with his "venomous" tongue and very bold character. MC may seem weak at first, but he's truly determined to get stronger, and trust me when I say that the author saves most of the golden fingers for him lol. Throughout the story, we'll follow his development and watch him grow into a fine soldier (still with occasional moments of abysmal EQ, but that's his adorable side I think). A nice thing is that both characters have almost equal screen time.
On the romance, hahahaha, both the ML and MC are mature in age, but they're greenhorns on the romantic front, so join them on a slow exploration of "what is love" and "do I actually like that guy". They naturally progress from haters to unwilling partners to friends to comrades, and eventually, to two boyfriends who are very supportive of each other. Oh and they have a very ~~cheesy~~ touching confession scene, almost the most unique confession that I've ever read about in BL.
Of course this novel isn't without its fault. Given the author's choice to go with rather realistic story-telling, the story might dive into lots of details and get a bit dry at certain points. But it is overall a very nice read, do give it a try if you're into action BL, or looking for a novel that has an interesting take on apocalypse.