I bought this mostly for the purpose of improving my rather mediocre German, but have been pleasantly surprised to find I have really enjoyed it. Rufus Beck's voice is very easy to listen to, and I find this audio version easier to understand than reading the book, because the sentence structure (always a bit of a handful in German!) is clearer when spoken.
I have also sampled the French Audio version (of the 3rd book) which I found a bit over-the-top, but this is read in a straight-forward, grown-up manner - not unlike Stephen Fry's English version, though I suspect it is not as 'posh'. Beck does different voices for the different characters, some more comical than others; the only one that grated was the unfortunate echo that is used to represent the Weasley twins speaking in unison. Lockhart's rich, confident voice is particularly well done, and overall the different personalities are well captured.
This version is 'mp3', which means the book is covered in just 2 discs, but needs to be played on a computer, or mp3-compatible CD player - I believe there is also an ordinary CD version available.