One Room is a masterpiece.
Let's start talking about each arc and it's characteristics.
The first arc features Hanasaka Yui as the heroine.

Yui is a young girl who is trying to get into college but has trouble studying, therefore she asks the protagonist for help, and this is where the story begins. This arc brings us 4 episodes full of emotions, with the development of the story, we can experience feelings such as happiness, sadness, anxiety, peace, and finally, love. Yui's very strong personality is what makes her such a captivating character, she is clear about her feelings and we can always sense that she is trying her best to achieve her goal.

Overall, I would rate this arc 6/10

Next, let us move up to the second arc.
The second arc features Momohara Natsuki as the heroine.

Natsuki is the protagonist's younger sister and is a character with a "tsundere" personality, which brings a lot of comedy into this arc. The story begins when Natsuki decides that she will live in the protagonist's house, in Tokyo, for a couple weeks in order to help him with his new, working life. There is something special about this arc that I would like to mention, it is that in the ending of each episode, Natsuki writes one of the "Natsuki rules for living" based in the events that ocurred in that episode. Disclaimer: This arc has a lot of feet.

Overall, I would rate this arc 7/10

Now, into the third and last arc.
The final arc features Aoshima Moka as heroine.

Moka is an aspirant musician who makes public concerts in the streets and fights to achieve her dream of becoming a sucessful musician. This arc is the most emotional one for me, because the heroine and the protagonist are childhood friends and they are both going through hard times in order to achieve their dreams, and this is the factor that brings them back together and also what makes this arc so special, I honestly could not avoid crying in the last episode.

Overall, I would rate this arc 9/10

In order to end this review, I would like to talk a little bit about my personal experience and enjoyment.
Each episode whas simply great, I could sense the characters discovering new emotions and growing affection for each other. Something that happened often is that I would pause the episodes to in order not to cry. I am writing this review right after finishing the show, and to be sincere, my eyes are still puffed.
That's it, I hope you liked my review!