It's about time that some decent attention is being given to matrix groups and Lie theory. I like the range of this book. However, there are better introductions. The main problem with this book is that its prerequisites are extremely unclear and its content is somewhat uneven. For example, it's hardly an undergraduate introduction if it needs a strong foundation in topology and a first reading doesn't seem to really require that or even some of the other concepts introduced. Sometimes when a concept is introduced, a theorem is stated or snatches of theory are brought in, the reader is left hanging without a more thorough contextual explanation or even a proof. For example, it's annoying to see a theorem stated and unproven without further comment and without any reference. The text might even be a little overwhelming for a first year graduate student. It would be difficult to teach a cogent and logically laid out course using the text. There are better introductory texts available now which are far more accessible to the intended audience. The author might want to do a little rewriting using Occam's Razor because it has the potential to be a more thorough intro than that available elsewhere.
On the plus side (more for the SUMS series than for any one book), having answers to the exercises helps the student immeasurably. In my opinion, any math text that has no answers to the exercises belongs to the last century and is either a reflection on the author's lack of industry or a basic fear that students would find little need to attend classes. But at this level of subject, we all know that attendance is directly proportional to the quality of the lecturer, not the quality of the text.