Bernstein's very very broadly paced rendition of Barber's Adagio is still unsurpassed for its almost painful emotional intensity and sublime beauty. When Bernstein takes a risk of extremely slow tempo, the music usually falls apart (the prime example; Elgar's Enigma Variation and Mahler's 2n & 8th), but with 'Adagio', it works! The way strings gradually build up the intensity and gather momentum is simply astounding and the long pause which follows the climax is awe-inspiring.
Rhapsody in Blue, with Bernstein at the piano, is also very impressive, with dazzling piano solo and powerfully expressive orchestra. What a superb pianist Bernstein was! He could have made a career as a concert pianist.