Stallings presents an updated education on cryptography. With a secondary emphasis on network security. In the cryptographic sections, there is a strong mathematical flavour. The narrative is not a high level, management-type discussion. It favours the professional mathematician and programmer, and ideally the intersection of these two skill sets.
Unlike some other books on cryptography, here considerable space is also given to hash functions. These can sometimes be used as an alternative to a full encrypt/decrypt approach. If you are designing a system, you should ponder carefully whether a hashing approach might suffice. Usually if you only need to authenticate a message or item. Since, as the book relates, for all the complexity of the various hash algorithms, hashing is far simpler and faster than public key encryption. And there is no problem with key revocation. Another great simplification.
The book covers the latest work on hashing. It appears that the 160 bit hash methods, like SHA-1, can now have collisions induced, as found by researchers at Tsinghua University. (Though the text doesn't appear to credit them.) Suggesting a migration to longer bit methods or to a more intricate method.
One surprising feature of this 4th edition is that PKI is mentioned here, unlike earlier editions. PKI has been around long enough and is important enough that I would've thought the 3rd edition of the book would have covered it.
The last sections of the book, on network and system security, are less mathematical. But to offset this, as it were, they require somewhat of a background in understanding the Internet Protocol and in the systems administration of a subnet of computers. Maybe the simplest advice to understand and implement is for a sysadmin to install and regularly run a password checker against the users' passwords.