I thought that the episode really captured that total disconnection from the real world you get with a new baby, which is why Alison was so distant with them. In that absence, you could see Mike stepping up and trying to communicate with them independently of Alison. I'm glad that there weren't any drawn-out goodbye scenes with the ghosts - there has already been so much evidence of those special one to one moments.
I also agree that it warrants a second viewing and is deeper the second time round - very much like the infamous episode of Motherland.
I thought they avoided mawkish and over-sentimental. The depth of feeling was portrayed so effectively in that scene in the kitchen at the end. You only needed to look at the faces of each ghost to see what that decision meant to each of them - plus those little asides from Thomas and Humphrey.
What an incredibly talented and intelligent goup of actors/writers - I have loved them ever since Horrible Histories! I wonder what the next project will be?