I'm recommending this 2-disc set because it's a sensible, cost-effective introduction to Wagner's masterpiece, Der Ring des Nibelungen, commonly called the Ring. The Ring is a sequential cycle of four operas, Das Rheingold, Die Walkure, Siegfried, and Gotterdammerung. With the exception of Das Rheingold, they are all of great length (Wagner was a colossal egotist who seemed to believe that no opera could be too long if he was its composer). As a result, acquiring and getting familiar with the entire Ring is an expensive and time-consuming proposition (my choice among complete Ring recordings, the landmark Solti/Vienna Philharmonic set on Decca/London, is 14 CDs costing around $1...-$...). Wagner purists will object to any attempt to excerpt "highlights" from the Ring, and they do have a point: unlike the standard Italian and French operas, which are readily divisible into recitatives, arias, duets, etc., the Wagner operas do not lend themselves to excerpting, with the result that "highlights" sets like this one are a collection of "bleeding chunks" torn from the body of the whole work.
Nevertheless there is a need for a way to approach the Ring, to be introduced to it and to get its flavor, and this generously filled 2-disc set fills that requirement reasonably well. (Wagner's six most important non-Ring operas are similarly if somewhat less generously highlighted on a Deutsche Grammophon 2-CD set that is a companion volume to this one, drawn from various Deutsche Grammophon complete opera recordings--none conducted by Karajan--so if you buy both sets--4 CDs--you gain at least some exposure to all ten major Wagner operas.)
CD 1 (76'33 in length) gives you 31'11 of Das Rheingold (1968), and 45'20 of Die Walkure (1967), which has long been the most popular of the four Ring operas. CD 2 (77'05 in length) gives you 25'56 of Siegfried (1969), and 51'03 of Gotterdammerung (1970). All the music here is drawn from the complete Karajan/Berlin Philharmonic Ring on Deutsche Grammophon (from studio recordings made in 1967-1970; the complete Karajan/Berlin Philharmonic Ring is 14 discs, price $1...-$...) The primary criticism of von Karajan's Ring when it was initially released was that his singers are quite uneven, and some of his casting is unconventional and controversial (in particular, his "artificial" casting is problematic, i.e., singers who were chosen for the recording studio but who might not be likely to sing their roles successfully in the opera house). In addition the casting is not consistent from one opera to the next (for example, there are two different Wotans, two different Siegfrieds, two different Brunnhildes; talk about changing horses in midstream!).
On this two-CD selection of highlights we get, obviously, only a very limited exposure to the singers of the complete Ring, but we can see what the criticism was all about. The Rhine maidens are excellent. Dietrich Fischer-Dieskau, great artist though he was in his proper sphere, unfortunately kept straying out of it, as he does here: Wotan calls for a Wagnerian Heldenbariton, which Fischer Dieskau certainly was not (any more than he was a Verdi or Puccini baritone). He is out of his depth here. Gerhard Stolze's idea of doing Loge is to talk, rant, and ham it up instead of sing (one wonders if he can sing). Gundula Janowitz is an appealing Sieglinde who sings well; she is lighter-voiced and hence more fragile-sounding than usually heard in the role. Jon Vickers and Thomas Stewart stand out as Siegmund and Wotan (the second one), offering impressive, well-sung performances. (Stewart also sings the Wanderer.) The Valkyries are a weak, underpowered bunch here (compare the lusty, superior Valkyries in the Solti or Bohm sets, for example). Helga Dernesch is a Brunnhilde with a big, healthy voice, good instincts, a comfortable middle, and an effortful top (she later wisely became a mezzo). She is not in the class of Flagstad, Traubel, or Nilsson, but apart from the problematic high notes I admire her Brunnhilde. Jess Thomas is conscientious in the cruelly demanding role of Siegfried, but his voice is basically unattractive and lacks the heft and heroic quality the role demands. (To be fair to him, there hasn't been a truly satisfying Siegfried since the great Lauritz Melchior retired in 1950, and Thomas is representative of the ersatz, makeshift Heldentenorizing we've had to make do with since then.) Helge Brilioth, the second Siegfried, in the little we hear from him here, reveals a more promising voice and sounds more like Siegfried should. The great attraction here is the orchestral playing and polish, which are most impressive, as one would expect from this celebrated team of orchestra and conductor who worked so long together. One has rarely heard the orchestral score so convincingly and painstakingly brought to life, and Karajan is considerate to his hothouse crew of singers, knowing how to scale his orchestra back to let them be heard.
This 2-CD set has direct, head-on competition from a similar (and similarly priced) Philips 2-CD set of highlights from the Ring. The Philips set preserves the Bayreuth "live" performances of the Ring of 1966-67 under Karl Bohm. One of its advantages is generally superior, more involved singing, including the great Birgit Nilsson as Brunnhilde, by singers who sing the same roles throughout (no switching horses in midstream) and who actually sang their roles in the opera house (not just in the recording studio). Also, since the performances are "live," there is a certain sense of vividness, immediacy, and excitement missing in a studio recording. On the other hand, the Karajan set offers generally superior conducting and orchestral playing; his studio recording can be more note-perfect (with its opportunities for re-takes); and the sound of Karajan's set is better than that of Bohm's live performances (although still not as good as Solti's Ring, or the best more recent opera recordings).
So, between the Karajan and Bohm 2-CD Ring highlights sets, there is not a clearcut winner. To make choosing more difficult, both are priced the same and both offer very generously filled CDs (both have about two and a half hours of music). I marginally prefer the Bohm "live" performances, but I couldn't argue with anyone who listened to them both and preferred the Karajan.