I first heard this recording as an excerpt (the ending of Act I, scene 5) featured on my Norton Anthology CDs for school. Immediately, I was blown away. I can honestly say that I have never heard a more emotional, more loving, and more heart-filled version of this Wagnerian masterpiece.
Nobody can beat the singing in this 1966 Bayreuth recording. Nilsson hits each note with astounding accuracy, especially those high Cs! Ludwig is also an exceptional Brangaene-- I must admit, though, that she does seem to overpower her mistress at some points.
Waechter's Kurwenal, in my opinion, transcends all other Kurwenals. He is simply unmatchable.
My favourite member in this cast, however, has to be Wolfgang Windgassen. As mentioned above, never, ever have I heard a more sensitive and emotional Tristan. He even surpasses the Tristan of Fritz Uhl, and believe me, that's saying something. His singing at the end of Act I totally blew me away-- having just downed the love potion, he responds to the wavering of Isolde's call with an overwhelmed emotion that I can't even beging to delve into. Beautiful, simply beautiful.
Though many have said that Boehm rushed the pace of this opera, I must diagree. I have listened to the Furtwaengler and Solti versions of "Tristan und Isolde", and they do tend to take the tempo at a slower pace that is almost dragging and unbearable. When it comes to the scenes featured at the end of Act I (the rushing, mixed emotions of utmost love, confusion, dismay, and fright after drinking the love potion) and the beginning of Act II (the hurling of the torch to the ground; the frivolous waving of Isolde and the rushing-in of Tristan to greet his lover). Karl Boehm has done an excellent job!
All-in-all, this is the best version of "Tristan und Isolde" that I have ever heard. In my opinion, it bests even the "classic" Furtwaengler recording, accompanied by Flagstad and Suthaus. If you are going to purchase "Tristan und Isolde", you couldn't ask for a better version.