One aspect of D&D 5e that I feel can be improved is mechanical PC differentiation after 3rd level. Spellcasters can select new spells, but by 4th level many subclasses effectively know what the next 17 levels are going to look like unless they multiclass. This book offers a copule different lightweight layers that you can place on top of your PC. It offers both additional flavor and roleplaying opportunity as well as ribbon abilities that are unlikely to break game balance.

First, the book presents a way in which PCs can evolve their Background, retaining small pieces of their former Backgrounds when doing so. It's a straightforward idea, but it goes a long way toward demonstrating the type of change a PC is likely to experience as they reach Tier 2 and Tier 3 play. I like how the PC doesn't completely throw away their former Background: they get to keep one aspect of it. And then they get to select a new Background that better represents who they are, now. They don't get the starting equipment from the new Background, but they gain its other features. This can happen twice: once during levels 1-10, and once during levels 11-20.

Second, the book describes 18 Advanced Backgrounds. Rather than reflecting a significant change in a PC's background over time, these represent an evolution of an existing Background. The PC doesn't lose the initial Background, but gain the Advanced Background on top of it. They're limited to just one Adavanced Background, so even if they're using the optional rule I mentioned above, they won't be able to take advantage of multiple Advanced Backgrounds (unless the DM wants to include that in their game, of course). Advanced Backgrounds have a bit of flavor text, then a feature that tends to be more focused on roleplaying and another that has more mechanical weight. A sidebar in the book encourages DMs and players to work together to mix-and-match the first and second feature to build a customized Advanced Background that's best suited to a PC.

The combination of Advanced Background features will go a long way toward covering a wide variety of PC archetypes. My only complaint about the book is that I want to see more Advanced Backgrounds. Thinking about my own PC, who has a Background that isn't in the PHB, I'd certainly need to work with m DM to build an appropriate Advanced Background. I'd likely need to ask if some of the ability scores could be swapped in features that target Intelligence or Wisdom when my PC has high Charisma. It's certainly doable, and I could change the flavor of the features to better fit, but that's a fair bit of change to place on the player and DM. Eighteen entries isn't an unreasonable number, and I understand that the book is focusing on PHB backgrounds (perhaps to leave room for future books?), but given that we currently have 85 official Backgrounds spread throughout the WotC books, there's certainly room for more Advanced Backgrounds.

I'm giving the book 5-stars because it does what it sets out to do: it offers new options to make Backgrounds more meaningful for your PC. It does this with new approaches and a deeper dive into the PHB backgrounds. It's left itself room for expansion—I would buy an additional book filled with Advanced Backgrounds.