The Bach of Helmut Walcha is different from all the others. He pays great attention to the expression of each voice, and the structure of the great organ works is also totally evident in his playing.
The fugues, particularly, are unique. Where other organists ruch to bring some animation to what may seem an endless sucession of entries of theme and countersubjects, Walcha just grabs the listeners attention to focus on the phantastic richness of expression and intelligence of the great fugues.
With Walcha, the whole takes precedence over the parts, so there are not rubatos over a short phrase. Instead, there is a perfect sense of structure, which is rendered possible by the greatest of controls on tempo, flexible over great stretches of music.
The chorals are similarly approached. One might prefer a more sentimental approach - particularly in the shorter pieces -, but if you listen carefully all the agogics he uses make the music perfectly clear, and extremely beautifull.
This is an archetypical vision of Bach. You might prefer a softer one, but you will not get a better one.
In a sense, Walcha reminds me of a pun an organist friend of mine often used to tell: In heaven, when God is present, the angels play Bach; when theyre alone, the play Mozart. This is the kind of Bach God likes to listen to.