I have not made my way through the entire set yet, but am moved to write about 7th and 9th.
The first movement of the 7th opens with tremendous energy. The second movement seems to stalk the nervously coughing audience, dancing its beautiful, ominous way among them.
The first time I heard the 9th was on my commute home. The third movement is sublime, heartbreaking -- I was just not ready for the affect it had on me. The music has such a gentle, compassionate, at times tragic voice, ultimately building in power to remind you that through the music you are touching the infinite, both terrible and beautiful beyond comprehension, and then returning to gentleness again after revealing the weight of its truth.
And then there's the historical context. I think that anyone who wants to gain insight into Germany, its extremes, brilliance, capacities for ecstacy and darkness, could do worse than experience this recording. I feel that I understand the country and its soul better for having heard this material.
The sound quality on the 7th and 9th is something you adapt to. For some reason the Germans taped with a high recording level so that the loud passages distorted. The sound on the 5th is much better. That said, Maggi Payne and M&A have done a superb job of reconstructing the sound from these early tape recordings. I'm very grateful to them for doing this important work.
As an aside, it's interesting to read Furtwangler's response to those advocating a literal approach to interpreting Beethoven in the accompanying notes.