As the owner of a great many books on control systems, I obviously have a favourite and it's this. It's a pity that it's currently out of print as this book provides the reader with considerable insight and hence a deeper understanding of control theory, from a state-space view point, than most. However, it is a little out-of-the-ordinary when compared to the usual UG text book on control systems.
To start with please note its sub-title: "An introduction to state-space methods". The book starts with examples of how to model various systems in state-space form, including using Lagrange's equations, which are of great benefit to a system modeller.
The book then considers system dynamics and frequency response analyses using a state-space representation. Again this approach offers real insight. Much of the more conventional transfer-function stuff is covered in this area (Nyquist, Bode, stability, Routh-Hurwitz). By now we're half way through the book.
The second half of the book goes into modern control theory, with an excellent explanantion of controllability/observability, how to design controllers (linear constant state feedback), linear observers and separation principle.
The really interesting stuff follows: Firstly Friedland considers optimal control (linear quadratic) and his derivation of the regulator gains is clear and thoroughly understandable. He then introduces stochastic systems and these two pave the way for a complete explanation of Kalman filters as optimum observers.
So the book tells a story. If you want to understand what modern and optimal control is (for linear systems), I think there's no better book.
It does not cover discrete time control or non-linear systems. And it does not go deeply into multivariable control system design. But this all helps to keep the book focussed.
There are plenty of good exercises and worked examples.
There are some minor (trivial) omissions and this book would probably not be suitable if you only wanted one control book, unless your lecturer had based his/her lectures purely on this one.
For me, this book ranks with Strang's "Linear Algebra and It's Applications" as a good read into a very deep subject.