Instruct: Classify the given Amazon review as either positive or negative.
Query: A Mengelberg MUST

This Pearl release is an absolute must. It contains some of the greatest orchestral recordings ever made. The original recordings -- in Mark Obert-Thorn's transfers -- are amazing for the 1926-1932 period, when Columbia made them.Mengelberg's renditions of Tchaikovsky's Fourth (1929) and Fifth (1928) Symphonies must be heard in order to be believed. The warmth of the sound, the wisdom of the orchestral balances, the beauty and incredible extent of the rubatos, everything is supposed to assure to these performances a unique place in the history of the recorded music. Almost every ulterior performance (except perhaps Koussevitzky or Stokowski) will seem shallow to you...