I too am an A Level classics/ancient history student and I ordered this book as it is on the OCR specification and also their exam examples have all previously been found in this book! It was incredibly useful for revision but could not be soley relied on for a wide range of knowledge. One thing that bugged me was that instead of giving hypotheses for reasosn why something was built/how/where/etc. it simply would give the answer "nobody knows!". I would say that it is best used with 'Roman Britian' by Guy de la Bédoyère (the book that was prescribed as the text for the course by my college) to give the level of knowledged required for an A2 exam on Roman Britain.
Although it is required by OCR to use this book for exams at A Level it is largely inadequate for the purposes of the course. It contains the bare minimum of information required to pass the exam and is over simplified to an extent that the reader is often left clueless as to what the meaning of the passage is. The book assumes that the reader has little intelligence and does not excite the will to learn the subject. For a far more informative, easy read that covers all the areas of Roman Britain (from the Iron Age to the final days of the Romano British people) I strongly suggest you could no better than read 'Roman Britain- A New History' by Guy de la Bedoyere.
Anyone doing a Roman Britain course at A-Level should definetly buy this book and use it. It has heled me during the lessons and also when writing up essays. It is useful when it comes to the revising part of the College year, and the insciptions and picture evidence provided are good when you need to refer to specific evidence in the exam. A must buy if you want to succeed in a Roman Britain course.