I second everything that all previous reviewers have said about this recording - it is one of the most powerful performances of any Mahler symphony I have heard. Before buying this recording, I owned the old Klemperer EMI and a rare release of Barbirolli and the Berlin Phil on Testament - both of these recordings are marvelous in their own ways, Klemperer for his driven, stark and unsentimental reading, Barbirolli for that special warmth that only he could bring to Mahler. The LPO and Tennstedt however are in another league. Recorded live in Feb 1989, this recording not only has amazing sound quality (you can really hear the inner details of Mahler's orchestration - more so than in the Klemperer or Rattle recordings), but also sounds 'natural', considering the restrictions of the acoustic from the old Royal Festival Hall.
By looking at the timings of each movement, you may think that it is stretched just a bit too much. All I can say is - IGNORE timings - they tell you nothing whatsoever about how dynamic and colourful a performance can be. I once heard a comment that 'the wrong tempo in the right hands can work', simply because of the genuine conviction that the conductor and players bring to the performance. (By 'wrong', I think the person meant 'unconventional', whatever that is...!) Anyway, that's irrelevant here. The LPO play superbly - creating an amazingly rapt tone in the strings when needed, and tremendous bite and articulation in the wind and brass - it made me think that they really were a world-class orchestra under Tennstedt. Just listen to the closing few minutes of the 1st movement - the amazing portamento in the strings will melt your heart - in fact there are several places in the symphony where Tennstedt gets the strings to play in an 'older' style, employing more portamento and rubato than you usually hear in recordings since the 1960s. Yet the LPO also produces a deliberately rugged sound when needed - sometimes I think many performances of Mahler nowadays are just too polite, as though conductors are afraid to confront the demons in the basement.
For me, Tennstedt's interpretation of the 1st, 2nd and 5th movements are a revelation (the 3rd and 4th are also fantastic, but perhaps a bit more predictable). Unless you know Tennstedt's way with Mahler, you really won't know where the tempo is going, such is his bar-to-bar control over proceedings. Occasionally you might feel that a few places don't work, but hey, that's the risk of live performance and that's what we all live for!
In short - stunning, sublime and revelatory. Need I say more?