I'm going to be honest: I didn't have that high of an expectation for this manga, the moment I first picked it up, but since I had nothing better to do at the time, I decided to give it a shot, and boy, am I glad I did so! This manga is one of those shiny gems that you find in the middle of others that don't shine, taking a concept that has already been used a couple of times, and cleverly giving it a whole new meaning. Also, don't avoid to notice how this manga is classified as "Psychological". It certainly won't disapoint you in that department, as the setting is absolutely shiver enducing (specially in [**SPOILER**] chapter 33, where Isao suffers from a psychological trauma). Now, let's jump into the review itself (may contain spoilers, read at your own risk!):

STORY (10):
This is perhaps, as I've mentioned before, the most appealing part of the manga to me. Komori Isao has been a hikikomori ever since he's stopped going to University, because of his inability to make friends. His first year was sad and frustrating for him, because of that, but he kept struggling through until the beginning of the second year. If you suffer from any kind of social anxiety, you'll know exactly how he felt, as he was looked down upon by the other students, and (I'm guessing, as it's not mentioned in the manga) made fun of, as he arrived at the entrance of the University. At that moment, his feet locked on: he realized he was unable to step inside, and ran home, where he has been ever since... What is life, may I ask you? Isn't it just a countdown before death? What's the point of living, when there's nothing out there? That's what every hikikomori asks himself, and would like to shout out as loud as they could to every person who's living a "normal life". But this manga assumes something that those who live a "normal life" fail to realize: they are just deceiving themselves, trying to act differently from their usual selves in front of others, in order to keep a social status. Isn't that Hell? Is that even living a "normal life"? That's where people like Yoshizaki Mari come in. People who have realized they are in a living Hell, and have realized their lives are not any different from those of a hikikomori: they are unable to have fun, they are unable to feel any actual happiness, they are unable to extend their wings as far as the wind blows; they are stuck in a hailstorm, being forced to protect themselves with their wings. And thus, Isao became Mari, who thought and felt exactly just like him. They aren't any different from one another. Actually, they were the same person all along.

ART (8):
The art certainly wasn't bad; in fact, it was really good! Even so, it wasn't on the same level of manga like Death Note. ...But they're different genres... I guess I really don't have a lot more to say about it, other than I enjoyed it. I suppose you can say you were able to truly appreciate on chapter 33. You'll see what I mean by then!

CHARACTER (8):
Man, I kind of ruined this section of the review with the STORY... Lol. I already explained everything I had to say about Komori Isao and Yoshizaki Mari, so, I guess the remaining main character to review is Kakiguchi Yori. She's much like Isao, in the sense that she was also a stalker, her life was horrible (since she had no friends) and she also viewed Mari as her only beacon of hope, although she somehow had a much darker aura... Perhaps because she wasn't the chosen one to become Mari, since she was her crush? Whatever the cause may be, she's certainly not your average comic relief; in fact, she's the opposite, really!

ENJOYMENT (10):
It took me less than an hour to read all the already published and properly translated chapters, and in the same day, I am writing this review. It's quite clear I REALLY enjoyed this manga. Please, do read it!

OVERALL (9):
Summing up all the points I've rated it so far, my final score for Boku wa Mari no Naka is a 9! Great job, Oshimi-sensei!

ADDTIONAL NOTES:
If I was to predict a possible ending for the manga, I'd say Isao (in Mari's body) would start dating himself, as weird as that may sound; but hey, this is a Psychological manga, isn't it? Another possible ending, and perhaps the most likely one, would be everything returning to normal, and Isao would date Mari. Although, where would Yori fit in that? Maybe take advantage of the Ecchi genre, if you know what I mean? I'LL SAY NO MORE.