This manhwa succeeds at one thing: creating the experience of an action-packed martial arts summer blockbuster movie: something that Steven Seagal, Jason Statham, or the like would star in. The majority of characters are middle-aged military vets, and the plot is merely a vehicle to introduce a bunch of them and have them fight it out. I haven't read anything else that specifically goes for and nails that vibe and experience, so I'd recommend at least reading the first season for the novelty.
Beyond that, each season is basically a new "movie" in this franchise of summer blockbuster with the same kind of action, same vibes, and little to no developments for any of the characters. What you are getting in the first season is essentially what you'll keep getting going forward, so if you're down with that, keep on going. If you expect anything more, you'll end up disappointed, as prior commenters in this thread have.