Note that on Viki this is titled "Fanletter, Please."
I am rating this knowing it is a 4-episode series. It can't be judged like one would judge a 16 episode series, where they have much more time to develop the story, background, and characters. It is more like a movie than a series, time wise.
The story itself is nothing special, but it is cute. I like the premise.
I am always amazed at the child actors in Kdramas - just how good they are. That was one reason I wanted to watch this series - it looked like it featured a child as a core part of the story. And it did, and the kid, or actually all the kids, were amazing! The ML's daughter was so darn cute I bet she'll be a star for a very long time.
I really like the execution of the story and really enjoyed the acting. If was fun! Yes, it had the requisite backstory of drama and trauma, but it was handled tastefully and did not dominate the story.
I want to avoid spoilers, so I'll just say I enjoyed this short series and I would recommend you give a try if you are looking for something short and sweet.