“In Depth” is indeed a reference; it covers a good bit more than either of the MoL books.
“In Action” is very much Bruce’s view of PowerShell, which can be useful. I find there’s a non-trivial amount of duplication of the help file content, although in some cases there’s some additional insight.
“Deep Dives” definitely covers some niche stuff, which can be very cool.
Bigger question: why do you feel it’s time for another book? Have you started writing tools and so forth? What do you feel you may be missing, in your knowledge set? Are those things best learned through less-structured experimentation and self-guided learning, rather than a book?
You bring up a good point. Maybe it’s not necessary for another book right away. I’m halfway through the MOL Toolmaking book and have just begun writing tools. I guess I always feel that there should be some next book to read. But it does seem like a good next step to take some time away from structured learning and spend more time doing.
PowerShell in Depth is as it states an in depth look at PowerShell - it covers much more than the MoL books. It really starts where they stop.
PowerShell in Action is a book about the PowerShell language written from, and very much for, a developer view point. Given that there is a new edition on the way (don’t bet on December as we’re still writing) I’d recommend reading that after PowerShell in Depth.
Windows PowerShell Step by Step (2015): written by Ed Wilson. Ed’s Step by Step is an introductory level book like the MoL books
Windows PowerShell Best Practices (2014): written by Ed Wilson. Has some very useful guidance but is not too much more advanced than what you’ve already read
PowerShell Deep Dives (2013): is a mixed bag of content. It was written as a set of short pieces by the PowerShell Community - ALL Royalties go to Save the Children so I’d recommend everyone who uses PowerShell should buy a copy
if your learning style is book based then I think the in Depth book followed by the new edition of in Action would be a good way to go. The Deep Dives is worth getting but its a collection of stuff rather than a coherent look at PowerShell.
To be totally transparent I’m the co-author of PowerShell in Depth, PowerShell in Action and contributed and was a section editor for PowerShell Deep Dives
Instead of a book, I would actually advise you scan GitHub for PowerShell repositories.
See how others write tools and try to understand from reading their code what their thoughts were creating that repo.
If you find anything interesting , try improving it and working with the repo owner.
Start your own repo, publish your tools, someone like you might be scanning and helping you get your skills to a higher level.