wa alaykum us-Salaam
I think the best way to judge books is by looking at the credentials/qualifications/teachers, etc of the author as opposed to just the content. i find this is usually the key to a good book/article/lecture, etc.
Sometimes people come highly recommended but they are not very scholarly or even good people for that matter (as I have just read a disturbing story in the advise and support section) How many books have I read by 'western scholars' who were nothing more than petty orientalists perpetuating the propaganda of 'moongods' and 'Arab invasions' -- I have always wanted a good book on the science of hadith and I have one called 'On Sachacht's origins of Mohammedan jurisprudence' and as the title suggests Dr. Al 'Azami is just taking on an orientalist, in and of itself is great but I want an excellent book on the compilation in details rather than dealing with orientalist bull which never ends..
the information is from a book by Bilal Phillips on usool al hadith. Also you can get all the material from this book by enrolling on a free short course at the Islamic Online uni, you'll get access to the book in PDF format, or you can just buy it.
Another good book is Studies in Early Hadith Literature. I haven't read it myself but heard it is good.