Disclaimer: I purchased this PDF as part of a Deal of the Day special, so while I did not pay the normal cover price, I did pay for it.
Now, Endzeitgeist has already done his usual outstanding job of examining the product, and most of the things he said I agree with. To put it into my own words, though...
As the name implies, this book is more than just a collection of traps. Now, don't get me wrong, having lots of traps is worthwhile in its own right, especially if your group is one where they'll actually go off now and then. I wouldn't advocate instant-death traps being a sure-fire thing, but come on, what's the fun of putting them in if they never actually get triggered? Trapsmith takes it a step further, though, by guiding you through the process of sensibly setting and using traps. In other words, you shouldn't just toss in a CR-appropriate trap and call it a day. Instead, think about which sorts of traps would be most sensible in a given way and build them up from there.
As a result, this book is useful for novices and veterans alike. Pages 21 and 22 are especially useful because they give a guideline for Perception and Disable Device DCs at each level, running from 'Easy' to 'Very Hard'. If you're not dealing with a min-maxing trap remover, these guidelines should be more than enough. Other useful parts of the book include advice on layering traps (why spring one when you can spring several?), making different kinds of traps more challenging, and even options for PCs who'd like to make some traps of their own. I'm particularly fond of the extra lock types that are harder for people to pick.
All in all, I think this is a great resource for gamemasters, and definitely worth picking up if you enjoy creating your own adventure locations. Overall, I'd rate this book about 4.5/5 overall, rounded up since I didn't feel there were any huge errors. I'm not sure it needed to have system neutral stuff on a few of the pages (this is a supplement for Pathfinder, after all, and it feels slightly out of place), but overall, I think this book is worth the price for the sort of GM who will actually use it.
[5 of 5 Stars!]