I'm going to start by saying that I've seen the entirety of this series, about three times. I can not actually boast that about a lot of shows, especially given the amount of time passing between watching it. This being my first review, I want it to be accurate and developed.
As far as sound goes, I've watched the dubbed version, and can find nothing wrong with the voice acting. It's one of those things that I typically can disregard so long as it isn't of a particularly annoying level. The music in the opening had me interested. I've always liked instrumentals, as they are different from the vast array of j-pop/rock openings that seem to be the norm these days. The effects are fine, and I don't much care that there is a lack of music for every scene, and honestly...that's a poor reason to dislike an anime. Crap music bringing good anime down, I can understand, but if it just isn't present, what does it matter?
The animation is smooth and fine. It takes something pretty god awful to make me think less of it, and if it provides a good story, then it can be overlooked. At least in this case, I think that they did a good job with the animation. It's as crisp as most that I've seen of its style, gore or no.
So, those are the two least important things to me in terms of reviews typically. The story is unfortunately brief which is a slight downfall, but when you've read the manga as well, you come to have an appreciation for the fact that they remain incredibly faithful to the original source material, despite not going into the depth that it had, which may be why so many seem to think little of the anime. There's no real end, and that is a real slight upon it, which I will not deny.
The blood and gore never bother me. I understood early on that this was an attempt by the creators to depict a more realistic (rather than constantly romanticized) version of the way Japan used to be. I appreciated that instantly, and understood that to be the reason for sometimes over the top violence.
Every act had its purpose, whether it seemed superfluous or not. Even if it was to simply show how horrible conditions may have been for those living in this period. Women were objects, and so they appear thusly. If you are offended by this, that's proper, but that doesn't mean the anime is in the wrong.
If you are very sensitive to blood and guts, you will not like this anime. In fact, you probably won't even give it a chance based on that alone. If you are too sensitive of mind or ideology, you probably won't like it either due to the fact that it's honest about life in the era, instead of putting a shiny deformed funimation face, with glomping on everyone and just borrowing the time as an excuse to give everybody swords.
I think the problem with most of the people who had serious problems with this anime try to claim there's a lack of story or characterization, but there actually isn't. It just isn't the story or characterization you like, with too many horrible situations to make you feel comfortable with the fact that you're watching a rendition of history that most anime doesn't bother with. The characters seem silent and background, because when you live a certain life, one dedicated to subservience, your individuality (a quality that today is seen as the most important and misread things on the planet) is something you put aside. The story itself is nothing necessarily extraordinary, but I believe its delivery is.
Any time you base a story around a group of individuals whose entire beings are centered around the perfection of their martial prowess, you are going to have a story with strife, and violence. It is a single minded pursuit, and that is why from the first episode, you see the primary characters Irako and Gennosuke come to be rivals. Make sure you understand that there are no good guys really. While the anime does more to portray Gennosuke as the protagonist, if you go into it thinking he's a superhero out to save kittens and undo unquestionable wrongs, you're an idiot. He's a man who had nothing other than the life given to him by Kogan, and that life is slowly tainted, and then ripped from him by the manipulating Irako. Now, while he's portrayed as the wholesale villain, he isn't. He is no saint, but he is no more a devil than any other man in this anime who is a practitioner of the martial arts, and who belongs to the same caste as he.
Again, I think the biggest problem, is that it is a narrowed down view of the manga. The manga gives more insight to the characters mentalities, allowing you to understand their personalities a little more, and it gives finality and explanations that are left horribly unexplained in the anime. Still, having seen this first, I couldn't help but be intrigued enough to want to know more. That doesn't happen very often with me honestly.
To touch on the animation again for a second, I've seen complaint about the use of stills and virtually no "animating" or some such. The thing is, I think this was part of the style that put me in mind of some of the samurai movies I'd seen in my youth. There's a lot of still moments, dead silences, and action ends in a matter of seconds. No long and drawn out bull shit back and forth blade clanging. Quick, decisive but thought out matches. When animators decide to use stills for action sequences, I think it's because trying to translate speeds is difficult, hence flashing lines in the background, and such. Then considering the level of skill that most of these characters are supposed to have, I can only view it as a stylistic decision. I find no more fault with it than how many action anime have recycled or constantly repetitious (or even meaningless) action "flurries" that really don't translate much at all. I suppose not having to see things in constant motion just to keep my attention has never been a strong suit of mine.
Bottom line: can this anime be offensive to viewers? Yes, especially if you're easily offended by blood and anything that doesn't try to paint everything in a pretty light. You will come to dislike something about just about every character, and feel badly for a great many of the non-central ones as well. You may be disturbed by the violence, but as long as you don't let that cloud your ability to see why it is present, you should be able to keep along with the story. You will have strong feelings one way or the other about this anime (so it would seem judging by other reviews) and as such, I think that's a positive in itself. There are enough anime that are so mediocre that I just don't care at all, one way or the other. Hate, is even better than apathy. But hate is certainly not my feeling towards it. The story progresses slowly, but it does progress until that untimly and abrupt end, leaving those who have appreciated what was told thus far yearning for more, wanting to know who will win, and how they both came to be there. Seeing a bit of the end first and then going to the beginning was brilliant, but leaving out a vast majority of the middle was not. Do yourself a favor...use this anime as a sampler, and if you were interested, read the manga.