The recording by which I got to know this opera was Karajan's 1970s recording with Helga Dernesch and Jon Vickers. Some of my comments on this recording are made in comparison with that recording.
Karajan conducted a brilliant, hard driven performance that is very exciting to listen to. In comparison, I found Bernstein to be more thoughtful, gentler and more willing to let the singers express themselves more. I have never found the opening numbers of the first act so ravishing to listen to as on this recording. It was also a stroke of genius to insert the Overture, Leonora III, just before the Act II finale. It works perfectly in mood and context and feels absolutely right.
The singers are all pretty wonderful. Gundula Janowitz is not a typical Fidelio; most are big Wagnerians, but she copes very well with the vocal demands of the part and (in comparison with the recording she as made with Karajan) really makes something of the words she sings. Lucia Popp is in lovely as Marzelline. The sounds she makes, even more so in ensembles with Janowitz, are pure aural joy. The Jaquino on this recording, Adolf Dallapozza, is a much more positive fuller voiced singer than many in this small part.
I am no so keen on Manfred Jungwith, the Rocco on this recording, but he is still pretty good. This is a very important part. He is the kindly everyman who can be made to commit murder on someone else's orders.
With Karajan, the action only really got underway with the entrance of Don Pizarro. He had a truly brilliant Hungarian baritone called Zoltan Kelemen in this role. Hans Sotin, as good as he is, did not convey the sheer menace of Pizarro quite so chillingly.
The Florestan on this recording is Rene Kollo. His entrance in Act II is a real tour de force aria. Kollo begins it with a long crescendo top G that really conveys the dreadfulness of his predicament. He is well able to convey the character's delirium later in the aria - stunning vocal acting!
The last main character to appear, Don Fernando, is usually sung by a bass rather than a baritone, but when that baritone is Dietrich Fischer Dieskau, I cannot really complain. As ever, he is able to convey the character's stature and importance.
In all, highly recommended.