This is a perfect, faithful translation of the original English text. This is rare, indeed, as many series that have gained fame of massive proportions often bring with them devoted followers who declare that any translations simply "aren't the same." This book IS the same as the English text; indeed, the only differences I found were with name choices, which I viewed to be a positive because they are clever representations of the characters just as JK used Latin to represent the characters with their English names. If you are looking to improve your French grammar, reading ability, or simply looking to reexperience the Harry Potter phenomenon, this is the book for you.
That being said, the price is steep. Let me recommend this. Look on amazon.fr or amazon.ca to buy the French version from either France or Canada. You may pay a bit more on shipping but depending where you live (I live near DC), I've found that you can often get a dramatic reduction on the price, which is, of course, unreasonable at this rate, even for a translation.
On the whole, this is highly recommended!