Spoiler free review (yay) - Beware broken English though.
Gwi is an awesome manga so it is with great pleasure that I give it a 9/10. Please note that this refers to how much I liked the manga, my personal opinion may differ from that of a professional reviewer.
What is there to like about this manga you ask? Well, first of all the art style is unique in the sense that I (in my somewhat limited experience) can't say I have ever seen anyone else do it exactly like this. It's simple in the sense that you can always tell exactly what is happening, it's strong
in personality and most of all it is "sharp". Perhaps the truest way i have to classify this art style is as "a type of art that is realistic in terms of human proportions, accenting only its fulcral design points to enhance the overall visual appeal".
The story is not over complicated, or perhaps I should refer to it as not being too simple nor too complex. It's simple enough that you don't have to think outside of your reading session to fully understand it while being complex enough to keep you wanting more and to surprise you at the right moments. At times the build-up may seem long and hard to keep up with but in the end no question remains unanswered; the "prestige" so to say is well worth the wait.
The important characters around which the plot revolves are relatively scarce in number but that is only normal in a short manga like this. One thing I must denote is how well they are portrayed, each with their unique personality and mannerisms that you can easily connect with.
Another thing I deeply respect in this manga is its adult tone. No ecchi, no comic relief, and most of all, no-bullshit. This is a serious story for serious people who don't care for the mundane clichés we are all so used to. Being a fan of all types of action manga set in different past eras (from feudal japan through the industrial revolution) and following sword wielding heroes, this was all I craved for at the end of the day.
Conclusion: If you are looking for quick, short manga with plenty of badass swordsman action and an engaging story then you will find yourself at home reading Gwi. A realistic and "sharp" art style, a great story and well portrayed characters are all things you have to look forward to when reading it.