I've listened to this twice now. My short review: Bernstein still owns the 6th.
Get the easy part out of the way: the recorded sound is tremendous. Clear as could be. You hear inner voices and other things often (usually) lost in studio and live recordings. The harp, so important in Mahler, is clearly audible - and often lost in every hall. The percussion is very present. There's no distortion and the engineers captured a very natural sound. Bravo.
The orchestral playing is (almost) beyond criticism. Intonation, phrasing, articulation are exquisitely handled and immaculate. Not one bit inferior to the big Mahler orchestras in the world. I especially liked the generous, appropriate, and beautiful use of string portamento.
Movement I: the opening tempo is, for my taste, too quick. Or more, it lacks the heaviness and sense of gravitas that it needs. And in the exposition (repeat taken) Dudamel shows what it is I find irritating about so many conductors of his generation. He seems to think that if he goes really slow at some points it will show that I understand the music better, and that it's more deeply felt. No, what it shows is that you don't know how to keep a musical line moving. This constant slowing down to ridiculous speeds, then suddenly going up tempo becomes really, really irritating and obnoxious. One of the masters of this symphony, like Bernstein, doesn't pull the tempo out of shape like taffy and finds far more depth.
II: to each his own I guess, but I prefer the SA order. The Andante is quite beautiful, string playing superb, and that utterly breathtakingly beautiful section in the middle is marvelously handled.
III: too fast, then too slow, then fast. Percussion, especially cymbals too loud. Cowbells sound great! And the closing passage is well done. Contrabassoon sounds great.
IV: Great atmosphere at the opening. Somewhere before the first hammer blow, a trumpet (?) entered early and ensemble got messy for a bit. I need to check with a score, but no time now. But something's not right. But then it seems like the Dude went to sleep, lost focus and direction. I think that's one danger of playing AS - that long, hard last movement is tough after the scherzo, and doing the SA gives the orchestra a bit of a breather. Throughout the finale though, I never felt the impending sense of doom. Never felt a catastrophe in the future. It all sounds right and nice, but the anger and relentless sense of doom that others bring is missing. One very nice thing: in some recordings that last big chord is often ruined a bit by the conductors who give a big, audible upbeat cuing the listener what's coming. Not so here.
Then -- what's wrong with LA audiences? Couldn't you hold the applause for just a few moments and let what you've just been through sink in? Blame the Dude - he could (and should have) held his arms up to keep the audience at bay. Too bad.
So, it goes through all the motions but Mahler needs more. In fact, you can have a lot of wrong notes, worse sound and still have a thrilling performance. That's what Bernstein (all three!), Barbirolli, Karajan, Solti, Tennstedt, Abbado, Mitropoulos and others bring to the table. To them, this symphony is about something; it's a life and death struggle and death wins this time. Dudamel isn't the worst, it's not even bad. More many people who like a lighter Mahler it will serve just fine. And maybe being there live would have projected a different opinion. But I wasn't at all impressed by hearing him in the First live in LA. His recent 7th on DG left me underwhelmed. I just am not yet convinced that Dudamel is a natural Mahler conductor.