This book is readable, well written and stimulating. There is a good deal of information and some well placed argumentation. It is stronger on the scientific and philosophical arguments. However there are weaknesses. Firstly the publishers blurb that this is a '21st century successor to C S Lewis's Mere Christianity, is a rather silly attempt to create a 'buzz and a vibe' about the book which if it were true, would not need such self publicity. Whats So Great About Christianity cannot be compared with Mere Christianity. It is nowhere near the same league.
Secondly the title itself is wrong. Christianity is not great - Christ is. In fact this is the biggest weakness of the book - in that it seems to equate Christianity with America and to some degree with right wing politics and social views. It is for that reason that the book will only really work within the US and even then only within a specific context. I doubt very much that it will be persuasive for those outwith that context.
Having said that there is a great deal of value in the book. D'Souza is intelligent, passionate and has a good understanding and grasp of the issues. If you recognise the limitations then this is a very useful book.