This manga has one of the biggest mixture of reviews I have seen, but for me personally, I give it a 10/10! It definitely isn't for everyone, but it immediately captured my attention and maintained it through its entire 15 volumes. I have read this story twice now, and it still has one of the most interesting and unique plots I have indulged myself in.
The author explores social issues in a very captivating way, and you can feel yourself relating to the main character. Yamamoto continuously made his characters choose very extreme routes which would then lead to unveiling very deep-rooted emotions because of the decisions they made. He knew what he was doing, from beginning to end - it is a very original storyline with very realistic depictions of the characters. Homunculus also stands out in my list for its artwork, Yamamoto went above and beyond for the visual storytelling. He chose very unique angles and views to draw from. There are little things in the background that add a nice touch to the atmosphere and setting. Everything you can see in this work is intentional and precise. And of course, the facial expressions... they are absolutely amazing. The world of homunculi that is brought to life in this manga is just mesmerizing, the amount of detail and research that was put into this story is far more than outstanding.
If you are a fan of "Oyasumi PunPun" (or any of Inio Asano's works), then I think you will enjoy Homunculus! They don't have very much in common aside from exploring a very dark psychological storyline; but they seem to be the most similar from what I have read so far as far as tone and atmosphere goes.
Like I said before, this manga is not for everyone. It was a mature manga with disturbing and grotesque themes. If you are comfortable with dark storylines such as Berserk, Old Boy, Monster, Gantz, I Am A Hero, Blood on the Tracks, or Flowers of Evil, then I definitely suggest that you check out Homunculus if it interests you! However, if you are interested in this manga but are not familiar with heavily mature themes, then I do still recommend this manga, but perhaps do some research on the contents and trigger warnings!

This is one of the most unforgettable mangas I have ever read; and it has one of the most memorable and unforgettable endings I have ever seen. It truly makes you question reality, and look deep in yourself. I honestly believe Nakoshi is one of the most relatable characters I have ever known. False life, false women, false appearance, false money... what really matters to him? A man who has cut ties with society and chooses to live how he pleases. A man who lives in the middle of a contradicting society, between a high-end hotel that looks down on the homeless shelter is it built across from.

This manga brings up some interesting social, psychological, and theoretical questions.
Are we truly happy with where our lives are now? From the top of society to the very bottom, just how different are the rich from the poor? If we take the time to see people for who they really are, will anyone bother to do the same for us; or are we all truly selfish in the end?...