I need to reacquaint myself with some of the individual performances, but on the whole this is a strong set. Kubelik was congenitally incapable of phoning it in. Even where I disagree with his approach, he conducts persuasively. For example, he blazes through the first movement of M6 in 21:07 (with the repeat!) but somehow it just works.
Yes, the sound is a bit dry and dated, but inner voices register with unusual clarity. And, Kubelik divided the violin sections antiphonally throughout the set, which I think is always helpful in Mahler. Solti's CSO recordings sound opaque by comparison.
Recently, during an obsession with M8, I put on Kubelik thinking that the sound would be a joke compared to newer versions, and that I would just play the first few minutes. I was riveted from the first note and played the whole symphony without a break. This recording has always been noted for the excellence of the soloists, among its many virtues.
As a footnote, I think the first real orchestra concert I heard was Kubelik with "The Bavarian Symphony Orchestra of Munich" in Peoria in October of 1968. I was thirteen, and I managed to get Kubelik's autograph. On the program: Haydn 104, Double Concerto for Two String Orchestras, Piano and Tympani by Martinu (a work I adore to this day) and the Franck Symphony.