These recordings all exhibit the even-tempered clarity one associates with Ansermet's recordings of Debussy. I wanted, in particular, to comment on the 1957 recording of "La Mer" in this collection, as I originally got to know and love it in its guise as a "London Stereo Treasury" LP. Its sound, in common with a great many London early stereo recordings, featured a harsh-sounding frequency spike in the low-treble range (ca. 2.5 kHz). I suspect these recordings were originally mixed this way to compensate for common shortcomings in inexpensive hi-fi speakers of the day, but come off with a harsh, steely-sounding edge on more modern sound gear.
I was quite anxious to hear this beloved recording again when it came out on CD, but its first release as a budget-priced "London Weekend" CD was marked AAD, and indeed exhibited the very same harsh, steely-sounding spike at around 2.5 kHz which was all-too-familiar from the old Stereo Treasury LP.
In this later incarnation, however, in Decca's "Legendary Performances" series, it has obviously been remixed from the master tapes with a much more realistic and well-balanced equalization curve, and the difference is very gratifying. You can still find used copies of the London Weekend CD, but this is the one to get for this great recording of La Mer, in my view. It's a pity that Decca has let it go out of print already, but it can still be found used, and as a CD-R at ArkivMusic. I think this 1957 recording has also been released in one of the Australian "Eloquence" CDs, but I've not heard that one yet.