Really early Mahler recordings can be painful. (As can early Stravinsky or just about anyone, before orchestras got the music in their ears and fingers and could read and play them halfway decently.)
The most execrable Mahler I knew was this recording of the Sixth, the only one the school library had before the Leinsdorf and the Bernstein ones became known to us. It was 1968 and we had just experienced the Szell performances in Severance Hall, and this was all we had to go to for more. I always wondered how it came to be on the Epic label, but maybe they published a bunch of things like that, and who cares, really.