Of Maazel's Vienna M1, I think 'boring' is being polite. To my mind, it's the worst one in that cycle. His Vienna M8 has terric tam-tam smashes at the very end, and Richard Leech does a sensational job on the two big tenor solos in Part II; better than Rene Kollo, even. Unfortunately, so much of Maazel's M8 is predicatably 'under tempo' (slow, except for the end of Part II, which is almost too fast).
One Maazel Mahler disc I do like is the recording of songs with Waltraud Meier and the Bavarian Radio Orchestra (RCA). Even though Ms. Meier shows a bit of wear and tear, I really like her expressive - but not overly expressive! - singing in "Kindertotenlieder" and the few songs from "DKW". I love their rendition of "Wo die schone Trompeten blasen" (my favorite ballad from "DKW").