Just take a look at the cast, orchestra and conductor.
It's been written somewhere that this opera requires the four greatest singers in the world, and at the time (mid-50s), this cast would have come pretty near it. Herbert von Karajan's conducting suits the music perfectly and the chorus is excellent.
The only drawback in this set is the mono sound, which is fine for its age but not up to the standard of EMI's later stereo recordings. However, this matters less in this opera than others, firstly as the performance is so good, and secondly, as the orchestra is perhaps less important in terms of detail and colour than Verdi's other works. The mono sound is preferable to the old LP issue, which was 'electronically re-processed to simulate stereo' and sounded a bit strange in places.
Verdi's great music makes you forget the ridiculous plot, truly one of the worst in opera. Despite its age, this is still my favourite recording of this work.