I read Professor Mitchell's review with respect, having bought the 4-disc set. Anne-Sofie Mutter is a larger-than-life violinist whose interpretations can seem mannered, the interpretative quirks calling attention to themselves at the expense of the music. Such quirks do happen here, and it's a question of how you feel about them.
Undoubted positives first. She makes a beautiful sound, which she is capable of varying through a wide range of expression. She plays absolutely in tune, nearly always bang in the centre of the note. Her bowing control is as absolute as is humanly possible. There is no doubt that she takes these works seriously and treats them with the respect they deserve. She is partnered by a wonderful pianist whose contribution here is a big, big plus (and these are, after all, piano and violin sonatas, piano named first in Mozart's day), in most of which the pianist's role is to a greater or lesser extent greater than that of the violinist). The recording is perfect, I think, and as Professor Mitchell pointed out, the balance is excellent, as good as any I have ever heard in this combination of instruments.
I have played these sonatas for years and have several recordings, complete sets or of individual works - by Perlman, Accardo, Szymon Goldberg (a particular favourite), Grumiaux, Szeryng, Francescatti, Heifetz, Stern, Fabio Biondi, Andrew Manze, Rachel Podger and others. I think Ms Mutter 'messes about' with the music more than any of these. She lingers on the opening notes of some phrases. Sometime she rushes little semi-quaver scales. In repeated phrases, she will play without vibrato, the tone colourless, then tentatively using a little vibrato, then the full-on thing. Occasionally she plays a really rough, hard-edged chord (e.g in K.378). All of this is deliberate and calculated - she is completely in charge of what she does. If you like your Mozart 'straight', notes played accurately in steady, well-chosen tempi, you probably will find this a little hard to take, even if you marvel at Anne-Sofie's quality as a violinist.
However, I have to say that, after many listenings, I do not find that her rather personal approach palls. It is all done with great commitment and it nearly all works. There are very occasional moments when what she does seems contrived or just wrong (I don't at all like her skittish, arhythmical semi-quaver scale into the second subject of the first movement of K.378, for example - but then she plays the tune most beautifully and the deviant semi-quavers are forgotten), but nearly everything convinces me and bears repeated listening - and you always have the lovely sound, the varied colours, the absolute precision, the bowing control and so on. In addition, she is particularly good in the greatest of the Sonatas, for example, K.454 and K.304. Especially in K.304 I think she brings new insights.
DGG's presentation, as usual, focuses a lot on Anne-Sofie (an interview, many photos of her, looking left, looking right, laughing, looking intense, looking girlish, etc., and a cover picture which enables us to evaluate fully the aesthetic effect of her bottom). There are 17 pictures of her, 7 of Orkis ; she appears alone 11 times, he does so only twice, and while she has a 5-page interview, there is nothing about him at all. So I feel a little guilty writing so much about her and so little about him - let me put that right to a certain extent. He plays 'straighter' than she does, without any loss of expressiveness, power or excitement. His technical control is impressive. He allows himself to ornament phrases in a most diverting way in the earlier sonatas. I found his playing a delight from beginning to end. Three cheers for him!
I did wonder for a moment, finally, whether to give this four stars or five. The four would have been an anxious, indeed a craven acknowledgement that others might not like this as much as I do. But in the end, it's a five-star set for me, emphatically, and up there with Grumiaux, Goldberg and the best - complementing them and providing a different persepective, which is all to the good.