Tony Giddens is pretty much the best known sociologist in Britain today, and this is one of his earlier books, penned long before he began his march up his 'third way'.
The book has been used by countless students over the years as an adjunct to reading the works of Marx, Durkheim, and Weber, but is by no means a replacement for proper study. Some of Giddens' writing in this book is quite unhelpful, muddying the waters rather than helping the ideas settle in your mind. Indeed it is much easier to understand a fair few of the key ideas from the original texts than from Giddens' analysis! The book is not bad as such, but then it is not really that good for the purposes that most students want it for, namely to act as a kind of prompt and simplification to aid in the learning and understanding of the ideas of the big three.
Lee and Newby's 'The Problem of Sociology', Morrison's 'Marx, Durkheim, Weber', and Craib's 'Classical Social Theory', are all more accessible and make for a happier student. Just remember that all these books are not meant as a substitute for close reading and study of the real thing and you won't go wrong.