I have all three of Karajan recordings of the Requiem - the 1962, 1976 and the one in question - and the 1986 performance to my mind is the most compelling of the trio - and a strong contender in a crowded market.
Why? Well, firstly, much like his recordings of the Bruckner 7th (1970, 1976 & 1989), Herbie progressively sped up in this work over time. Each movement, by and large, is faster than its predecessors. This is an asset; the Bohm DG alternative is leaden by comparison. When abetted by the Vienna Philharmonic (which was a miraculous ensemble in the 1980s - and the timpanist has a field day, happily), it makes for wonderous results.
The soloists are not overly memorable (with the exception of Burchuladze in the Tuba Mirum) and the sound-engineers could have done better in certain instances (choir-wise, where are the sopranos and altos in the first movement?? - they are inaudible - but the rest of the performance is first-rate).
Even so, these are sunspots. Listen to the end of the Lacrymosa - it is genuinely elegaic. The Hostias, redolent with grace, is an antidote to the period-practice atrocities so often committed against this movement. The so-called Sussmayer elements in the work - insofar as they can be so labelled with certainty - blaze forth as if penned by the Master himself.
Make no mistake: those wanting a traditional recording of this masterpiece - in the best sense of that word - should not go past this recording, ne absorbeat eas tartarus, ne cadant in obscurum.