This is exactly the sort of book osprey should be publishing. Too many of their books attempt to cover vast areas of military history in 40-odd pages and end up being little more than a summary. Some appear to be little more than cut & paste works from other sources.
Although its the same length as every other Osprey its so detail heavy you don't end up feeling cheated. It sensibly covers only the STUG variants with high velocity guns: basically the Stug III F & G with the long 75mm cannon and the very similar Stug IV plus the infantry support variant with the 105mm howitzer. The authors at the very start specifiy which sources they used & which they discounted. As such the book is both specific and accurate. As the first reviewer says its probably not intended for the general reader, but I personally find this a good thing.
There are good photo illustrations throughout and unlike many books you will not find these pictures via google images. Generally the pictures are front aspect and mostly taken in Germany so they don't give a total picture of what a real combat STUG looked like but there are a few photos taken on the eastern front and the colour plates are well drawn and highly detailed. Some internal photos would have been nice, although there's a Finnish stug cut open which gives an idea of crew layout.
The book would benefit from a slightly more detailed breakdown of units that used the vehicles and some descriptions of combat would have been good too. Its primarily written about the actual vehicle with less emphasis on who used it and how. Basically if you want lots of technical details about late war Stugs this book should be your first purchase.