These books are a must to become grounded in the fundamentals and move beyond basic/beginner usage. You can go fairly intermediate with the language in about six months.
I’ve heard great things about PowerShell Cookbook, but I’ve never read it.
PowerShell in a Month of Lunches goes from “This is PowerShell” to “Here’s how to use it in a production environment.” PowerShell Scripting goes from “So you can do day to day sysadmin with PowerShell but why not automate your entire platform and implement version control? Keep reading to learn more!” – It goes into building modules, importing them into other scripts, version control, using PowerShell with SQL Server, writing automated tests for PowerShell, things like that.
The difference at a high level is it’s more dev focused, but you still learn a lot about PowerShell. The first book is how to check on servers and processes, more or less. The last shows you how to automate and test the previous book.