It must be tricky for the programme makers to get the balance between an interesting story and an engaging subject. Richard Osman is very engaging but the story wasn't particularly interesting, and there have been interesting stories about the families of celebrities who are annoying to watch.
One of my favourites was Jeremy Paxman, ages ago. his ancestors led very different lives from one another, and the researchers were able to go back quite far back. Paxman was visibly moved by what was found.
Some of them stick with one side of the family and concentrate on one incident, such as an experience in a particular battle. I prefer the ones where there is a lot of variety, but I guess it's the luck of the draw.