This book is a fundamental guide to develop the skills necessary to write powerful VHDL code.
The approach taken by this book is to provide only what you need to know to get up and running quickly in VHDL. As with all learning, once you have obtained and applied some useful information, it is much easier to build on what you know as opposed to continually adding information that is not directly applicable to the subjects at hand.
Really beginners book to VHDL, only covers the basic syntax, doesn't cover packages, testbenches, records, etc. I would say it's the perfect book if one never worked in HDL and wants a step by step guide on why describing hardware is not programming, how you should think in a concurrent way when designing and wants tons of exercises (with solutions, but no simulation or even a "how to" guide to simulate designs with open source tools such as ghdl).
After that I would highly recommend Circuit Design and Simulation with VHDL by V. Pedroni. To this day, it is still my go to reference. After that, look into VHDL 2008: Just the new stuff to write powerful testbenches.
This is a pretty hilarious primer - the author's must have had a laugh writing it. It was read as an accompaniment to an FPGA course in VHDL and was rifled through several times. Would recommend!