What can I say, other than if you enjoy anything related to ancient warfare, and especially China, that Kingdom is one of the best treat that you can get for yourself.

______________________

Enjoyment.

The enjoyment that you will get from this manga is simply off the chart. All you need is a bit of epic music in the background to accompany your reading (I recommend two steps from hell). Do not even bother watching the anime unless you feel the need to appoint some voices to your favourite characters (I do admit they didn't mess that up at least).

_______________________

Story and characters.

Now, what make this seinen war manga so good? It's simple, the main forces behind it are characters with enormous charismatic auras, paired with a gigantic scope. Yes, the scope of this manga is also what allowed it to run for so long (more than ten years now).
After all, right off the bat, we are told that the end goal is to unify China. I'm around 500 chapters, and there's still not even a hint of our protagonist to be even close to succeed yet. Of course it's not like they lost sight of the goal, but rather that in order to achieve this goal, the protagonists need some time to grow, each one of them.
So do not even worry about pacing or the manga losing steam because it doesn't.

Most of the characters are stereotyped, but they all feel genuine, and none of them are irritating which is a good point. You can pretty much root for anyone. (apart from a few very bad guys that are just there for the sake of being bad).
Some of the best characters of this manga are actually quite evil to reflect the time period, but even then you still love them, because they're badass.
I would also add that the majority of the characters have plot armour for obvious or historical reasons... so I guess going in without knowing too much about the warring states definitely is better, because sometimes you really don't know if someone is actually gonna get killed in action.

Another thing... what you will witness in this manga is that generals are basically super-heroes. It's actually completely normal, because these periods of china history are pretty much mythical. Do not worry, some components of ancient warfare remain realistic: the tactics, the maneuveurs, the actual time it takes to finish a battle or a siege involving thousands of soldiers. But generals... they will cut down in half men in armour, they will kill hundred of them, no problem. And you will love it.

______________________

Art

Now this isn't an art that I had ever seen before, it's typically "round", I guess. But it's still pleasantly good to the eye. And frankly, some scenes are simply breathtaking. "Epic" is probably too weak to depict some of these panels.

______________________

Conclusion:

I just hope this manga keeps going for another ten years. This is imo the work of at least half a lifetime. The warring states period is no joke, especially since you plan to finish your work when your story has a clear historic end. And to me if after 500 chapters the author still manages to make my heart race, then the next 500 will certainly do the same.