At first this drama brought up to me because my favorite idol singer was making acting comeback and i thought, "a drama about prison life? seems pretty decent but may be boring for my liking." But suddenly they had Shin Won Ho's name in articles so i expected something that would entertain me no matter what.
I watched the first episode raw so I didn't understand a thing and i'm not satisfied. Later on, when the subs were out, there were actually many witty dialogues and scenes that i can't catch when I was watching it raw and it received my like immediately.
The story is definitely the title, Wise Prison Life. The prison life actually frustrated me and made me think that there were no good person here since it was prison. But the characters aren't clearly black and white. Also they won't give you a saint main character. We either hate or love the main character.
Through reply series, I got to know how good Shin Won Ho is and this one won't prove that statement wrong. He didn't give you the over-the-top character and it is proven by how he made an unskilled actor to act decently. If it's otherwise, I'd drop immediately.
Also the cinematography is one of the reason why I love cable series more than non-cable series. There are no cheap fillers and each scenes had their own charms.
The music, wow, i realized i haven't downloaded osts for a while and only liked one or two osts from recent dramas but this one, each osts are so good and enjoyable. My personal favorites are heize's and of course Seungyoon and Mino's (please listen, everyone!)
I would definitely rewatch this since all the scenes are so hilarious, even the sad one would make me cry if i rewatch it.  
Overall it's 9 for me. I hope they have spin-off like reply series too