REFERENCE: My favourite Wagner‘s Operas

Tristan und Isolde is an opera in three acts by Richard Wagner to a German libretto by the composer, based on the romance by Gottfried von Strassburg, which in turn was based on the story of Tristan and Isolde incorporated into Arthurian legend from earlier interpretations of the somewhat obscure Celtic source. It was composed between 1857 and 1859 and received its first performance in Munich on June 10, 1865.
Many Wagnerian critics of the time claimed that the musical portion of the opera attained the highest summit of all music; on the other hand, an equally influential group of critics, centered around Eduard Hanslick, condemned the work as being incomprehensible.

Tannhäuser (Tannhäuser and the Singers' Contest on the Wartburg), an opera in three acts, music and text by Richard Wagner, based on the two Germanic legends of Tannhäuser and the song contest at Wartburg. Key themes are the struggle between sacred and profane love, and redemption through love (a theme running through almost all Wagner's mature work).