I only started watching Mr. Merman because I always want to check out mermaid/merman shows. Most of the time I'm disappointed with the CGI/costumes or with the story line in general. Mr. Merman...that was a surprise, and a welcome one at that.
The story itself sounded interesting in regards to the characters but it did not sound like something new. Well, in general it isn't. But, MM makes this simple story into so much more. The characters get enough back story so you can feel with them or they get enough screen time so you'll warm up to them easily. It starts off simple and gets more complicated later on without making the show too strange. It stays as down to earth as you can get with a merman show. Also note, MM is one of those dramas that have the perfect length. If it had been longer, the story would have been dragged out, if shorter, it would feel rushed. It was just perfect!

The cast was quite good and a little bit of a surprise. Here I have to say, I have never like the female characters in a show so much as in MM. The females aren't just weak or strong but the know what they want while also showing their weaknesses and standing proudly. They don't just fold because someone is pushing them. And they also have a good sense, which means there are almost no "give someone else the fault" misunderstandings between the six leads in the drama. That was refreshing!
The laugh of the doctor was strange though...especially around the later episodes.

About the music - it was too loud. There were almost no no-sound scenes. So put your speakers or headphones on low volume. You'll still hear everything but you won't get a headache from all the music.

I'm also definitely gonna rewatch that one ^.^ I recommend watching this if you are annoyed with the typical female leads, want to have a fresh supernatural drama, wanna see merman in a drama for once or want to try something new.