One can dispute that it is always great recordings of the century that EMI has reissued in its "Great Recordings of the Century" collection, but Bruno Walter's conducting of Mahler's 9th Symphony, recorded live in Vienna on January 13, 1938, certainly is. First, because it is the premiere recording of the symphony, Mahler's penultimate (that's counting the unfinished 10th), first sketched during the summer of 1908 as the composer was working on Das Lied von der Erde, then completed in draft form in the summer of 1909. Second, because Walter has unique legitimacy in this work. He was then Mahler's favorite disciple and there were long exchanges of correspondence between them in that period, although Henry-Louis de la Grange, in his mammoth Mahler biography, doesn't record that Walter discussed the score with the composer as he did with Das Lied. Finally, Walter premiered the piece on June 26, 1912, shortly after Mahler's death, and already with the Vienna Philharmonic. I hesitate to call Walter the closest recipient of Mahler's intentions as can be and his most truthful interpreter, not only because this recording dates from more than a quarter century after the premiere and almost thirty years after the work's completion and any possible conversation Walter might have had with Mahler about it, but also because Mahler himself considered that the composer's intentions were never definitive and were only those expressed on the day of performance. So there can be no certainty that Walter's interpretation in 1938 can give an idea of the way Mahler would have conducted it, had he not died. Still, there is a direct line between Walter and Mahler, that only Mengelberg - another early champion of Mahler's cause, much appreciated by the composer - can emulate; more important still, Walter's interpretation in 1938 is unique and special enough to substantiate at least the thought that this is as close as we've ever had to the way Mahler would have done it. It is far removed from any later interpretive paradigm in this piece, especially in its adoption of brisk tempi in the outer movements that (other than the maverick Scherchen in a recording made for the Austrian radio in 1950 but that was published only in 1990, Mahler: Symphony No. 9) no subsequent version that I know has paralleled, and it is filled with a unique emotional intensity.
But to hear all that you possibly can of it, despite the constricted 1938 sonics, you need to go to the 2004 remastering, Mahler: Symphony No. 9, which has considerably improved things over this previous one from 1989, with less swish noise and cracks from the 78rmp surfaces, more orchestral presence and much more impact given to the brass outbursts (but also a little more glare and harshness, and even a measure of saturation in some climaxes). You will also find my detailed review of Walter's interpretation under the 2004 remastering CD.