I'll talk about the 3 parts here so : the first part was fun and enjoyable, we really liked the underwater monster and the fact that we had to be really fast running away from it.
For the 2nd and 3rd DLC, we felt when playing that we didn't really know where we were going after a while, we were lost and didn't know what we were supposed to be doing. Some puzzles didn't make any sense to us : because of the designs (we believed that certain objects were meant for decoration and atmosphere like the books in the library) or because we were lost. During the 2nd DLC with the whole light bulb puzzle we had no idea what we were doing or where we were going and we had to the same routes a few times because of it.
As for the ghost children, I'm glad I found a controller because I don't think I could have done it with my mouse and keyboard.
At the end of the day the DLC is pretty good, the art direction was still really good although I would think about adding some accessibility settings or rework the light in some places where it's really too confusing.
The art, the music, the ending were definitely an highlight in our experience.