In 1963, the BPO was vastly more familiar with the Beethoven symphonies than M9. I think that the playing is quite good on Barbirolli's M9. It's a very pretty recording - easy to listen to - but I also feel that that's sort of the problem. To me, it simply isn't sharp-edged enough. If you're a big fan of Bruckner's music, I can certainly see how one would be drawn to this particular recording. I personally prefer a Rondo-Burlesque that's a bit more driven and angry sounding. To me, the best R-B is the one on the Bernstein/Concertgebouw M9. I also prefer that the fourth movement be stretched out a tad longer. But more to the point, it really should reflect sort of a zen-like, "otherworld"-liness quality. This is especially true in the more reflective passages, dominated by quiet woodwinds. To that end, I think that both Karajan and Abbado are somewhat better. But that said, I do feel that the Barbirolli M9 is very good for 1963 - especially with an orchestra that was not terribly comfortable with the idiom (and on some days, they can still sound that way). I don't remember what year the Bernstein/N.Y.P.O. M9 was made, but I do feel that it's a more "idiomatic" sounding recording.
Back in the first movement, I think that there needs to be more of a connection - or similarity - to the music of Alban Berg. The big (anti)climax should be absolutely terrifying. Mahler marks for the tam-tam stroke to be fortissimo, and he writes triple forte for the low brass. He also adds the words, "with the greatest possible force"! For me, Barbirolli comes up a tad short.
All this negativity stated, let me put this into perspective: the Barbirolli/BPO M9 was a huge improvement over the highly tauted (sp?) 1938 Walter/VPO M9, which was just awful on every account.