Hoo boy, there's a lot to unpack here. TLDR is that fans of modern fantasy, modern d20, or playing Pathfinder on a scale that keeps fear of the supernatural very real, this is the book for you.
The big thing that sticks out with this book is its size. Similar to some other Storm Bunny products, this book is incredibly extensive, clocking in at over 250 pages. Quite a bit of it is illustrated and tightly detailed, so you can expect to get quite a large bang for your buck. We've got a revised race system, some revised classes, a whole bunch of modern fantasy rules, and of course the oft-toted O7 rule system.
The O7 system (adapted from 3.5's old E6 rules) works great, creating a system of accelerated progression that makes characters feel powerful while keeping the dangers around them very real. The fact that the supplement offers a lot of details on how to accommodate a system of low-level gameplay into a high-fantasy game like Pathfinder is a nice touch. O7 is overall a very versatile, capable of being utilized in worlds far afield from the urban fantasy setting of BL&BM. I should mention, however, that the full alterations from O7 extend into the "Building your character" chapter of the book as well, so those wanting to utilize the full bevy of mechanics will have to check that chapter as well.
Now, let's get to the crunch itself. The first thing that needs to be talked about is the Bloodline system which replaces race, and I feel that this could be improved upon. Flavor-wise, the different heritages are all very distinct, with numerous lore tidbits being given for each and distinct flavor being established for every kind of character. The concept of custom-building bloodlin abilities through a point buy system is also fascinating. However, something that sticks out as distinctively lacking is the inability to customize ability score bonuses. This is particularly problematic when only one bloodline grants a strength bonus, a prospect which limits the number of viable strength-based builds.
The class list in this book is restricted, but this works to it's advantage. The open classes are Brawler, Investigator, Mesmerist, Occultist, Psychic, Slayer, and Spiritualist (although it seems implicit that Alchemist was supported at one point), seven classes which I feel do not get enough love. Many of them get new abilties at first level that suit the setting well, and the new archetypes for many of the classes are not only thematic but also fun to play. What's more, they are capable of being used in regular Pathfinder at low levels (high-level versions would be appreciated in future expansions should they occur).
In addition to bloodline and class, BL&BM introduces a third choice known as Careers. These determine your wealth and can grant a wide variety of potent non-combat bonuses if you progress enough in them (which is an entirely separate track from levelling up). It adds a modern aspect into the game without causing such rules to intrude on class functionality, and I could see quite a few games adapting it.
The system of feats and traits has received some revision in this book, and I feel that the changes are for the better. The use of a Tarot deck for deciding traits is darn creative, and the new and enhanced feats not only do a good job of making these options more suitable for modernized play but also more impactful on character concepts (Ability Training can actually boost your scores permanently, Demolition Training allows you to build and utilize all sorts of explosives, Weapon Proficiency feats now grant proficiency with multiple weapons every time you take them). Even better, these feats embrace creative strategic play, allowing the characters to utilize them in inventive combinations that offer a surprising amount of depth.
Equipment is also a consideration, and I feel that BL&BM does a good job of representing modern firearms in Pathfinder's ruleset. The sheer variety of weapons is impressive, allowing for players to customize their arsenal in some mechanically relevant ways. Armor, on the other hand, is less well-executed, with rules being ambiguous as to what guns (and melee weapons, for that matterr) can punch through what armor.
One final issue I have is that the PDF is poorly optimized and takes quite a while to load on my computer (a curse of the stylized design, I suppose). I'm hoping that this gets fixed up at some point.
Overall, there is a lot of good stuff here, and while some of it could use improvement I feel that there is more than enough fantastic content in this book to justify a purchase or run a campaign.