The main problem with this book is its level. It is a little bit too advanced for A-Level economics and yet a little bit too simple for first semester economics. Although it would be a good supplement to both A-Level and first semester courses.
Another aspect is that this book covers quite old models. Modern day microeconomics is mostly about game theory. Nowadays markets mostly get analysed in a game theoretic way. This is not to say that the material in Begg is wrong, but simply that the material in Begg does not provide quite as much insight about the economy as some of the modern approaches.
On the macro front, I must say that Begg is clearly an old fashioned Keynesian from 1960s. Modern day macro has moved far beyond old fashioned Keynesian viewpoint. Begg fails to cover modern research into RBC and some of the neo- and new-Keynesian models.
Begg should have also had a chapter on econometrics. Just a rough outline of the subject. I think an introduction into economics, such as Begg, should have had at least a mention of econometrics, which is a very important aspect of economics.
But still Begg is a good book. I would recommend this to any who has just finished A-Level in economics is about to start economics undergrad. If you read this book you will understand, although at a rather basic level, most of the material usually covered in first year economics course.