Gunslinger - they gave alternative options for other classes to do basically the same thing & that's really good enough. A new class wasn't needed.
Unless you go into advanced firearms, guns kinda suck, but any reasonable GM will run in the setup where guns aren't insanely expensive so at least cost isn't the issue & thankfully they didn't do rules for effects of blackpowder smoke in a dungeon.
Ninja - okay as a Rogue variant. My only complaint is that Light Steps is a freebie stock class feature instead of a talent like it should. That aside, contrary to what some reviewers have said, the choice between Rogue & Ninja is depends on your preferences. Both classes can pick up eachother's talents & they gave Rogue a Ki Pool talent.
As for the weapons gap. The Katana in this book isn't OP, trading general damage potential for a surprisingly appropriate utilitarian function, when compared to previous versions of the weapon, so no big deal guys.
Samurai - not needed as a class. Give me options for Fighter & Cavalier, maybe Monk(maybe). Concept achieved.
Feats: Some are good. Some are mediocre. There are a few that are overly specialized, so they're iffy on their value for PCs.
-Monk styles. I looked this over & the qualities vary greatly. Half the styles are pretty good & the other half suck. Some of that could be preference, but that would require another option. The good ones offer up enough of a sampling to make some balanced styles of your own, which is really good. All in all, I like them.
Weapons - several of them are nice. I like what they did with Katana instead of making it re-flavored Bastardsword, though it does give less reason to favor it over Wakizashi, as that's a light weapon & Katana isn't & the damage gap is negligible. Guns are only viable if you have the right set of cost rules(the price varies depending on the rarity of guns in the world)
Class variants - there are some okay ones, but some seem to be just desperate attempts at filling space. A few of the variants appear to be incomplete, such as Martial Artist Monk still getting Abundant Step, but is incapable of actually using it. There are other examples of this sort of oversight & it's kinda disappointing.
I honestly would like to see some variants that just trade off particular class features only which would allow for a bit more character customization.
Overall, it's okay. Some things are incomplete & the balance is lacking in certain things. You can use it if you've got the sense to exclude the broken stuff. I'd recommend the PDF, but it's not something the average player should rush to get a hard copy of anytime soon, as the PDF can be replaced with a downloaded update. Hopefully, Paizo can get their act together & work on this.