Every one of these tittles does contribute to the games of DM who want well written and tested rules for everything, such as me.
Comprehensive equipment gives me +200 hundred pages of illustrated weapons, armor, tools... for whenever a player complains about don't find in the manual what he is thinking about, plus some new cool mechanics. We can consider this the counterpart of the Monster Manual for equipment.
Comprehensive animal handling is just a new world of mechanics to handle this kind of companions. How they act, how can be trained, what they can do and how... animals stop being a stats-block in the grid and become fully interactive characters. It may be my favorite since in the basic rules they are... one page rule of mounts and an ability nobody uses.
Comprehensive wealth take the points in everything money-related. In basic rules they stop making sense when you get the point in which a resurrection spell costs you spare coins. Here you can build armies and warships, and the rules of armies combat just make sense.
Finally, I think Expanded Special Feature is a good narrative complement to give unique magic items with story and personality. No more “Here you have a +1 sword”.
I'm quite pleased with these supplements which will be used in my table. I'm looking forward new content from this author.