Don Ottavio's last aria It is nearly a countersense that one of the most inept characters in Mozart's operas gets one of the most beautiful love arias Mozart ever made.
And it's even odder thinking that this is not a love aria properly speaking. What would you say to someone that's asking his friends to take care of HIS woman? Surely he deservers to be a cuckold... (it reminds me Mr. Ford in Verdi's Falstaff: "Due rami enormi crescon sulla mia testa!" "two enormous branches grow on my head!").
This aria is divided in two parts, but it's not the like the usual da capo aria (A B A: the most frequent in italian opera, but not the only one), instead its structure is A B A B, where A is the soft, gentle part "Il mio tesoro intanto" - "My sweetheart in the meantime", and the B part is the wannabe furious "Ditele che i suoi torti" - "Tell her that her wrongs/I'm going to avenge".
The "soft" part is exceptionally tender, even if one can't help laughing because of what I already said, with second violins playing a beautiful and smooth quaver background with the mute on and the cellos marking tenderly the beats and the capital notes in the harmony with their pizzicato. Over this, first violins and clarinets expose the wonderful theme which, like a lot of the most beautiful and simpler themes in musical history, is made by joined pitches (B and E are flat: B, B, C, B,A, G, A, B, C, D).
The second part is more full of dynamical contrasts (e.g. a lot of fortepiano), a broadened extension stressed by a lot of arpeggios made by the strings, even fast ones (and on tensive chords like a dominant with the seventh), and fast and brief descending scales in pianoforte style.
I think that Mozart is exceptionally skillful here in keeping thin the orchestral support to the tenor "fury", which sounds kind of inappropriate, as if Don Ottavio was unable to act but only to menace. The orchestral closing only is strong and rich in body, like he's afraid of speaking, but when he doesn't speak loud he can act like a hero.
My favourite interpreter Believe me when I say that I heard a lot of Don Giovanni. I even played it once (as rank and file:-). I've never ever heard a performance as good as that of Luigi Alva in Carlo Maria Giulini's recording. It's perfectly clean, musically correct and almost always we feel like he's singing effortless. He also does everything calmly, avoiding the risk to compromise the result because of rage (especially in the second part of the aria).
I can also spend a good word about Hans Peter Blochwitz in Nikolaus Harnoncourt's edition - a really good version of Mozart's masterpiece - but tempo is in my opinion a trifle too fast. Even if it's evidently faster than Giulini's, it's not really different from a lot of other conductors' tempo: it's a matter of a few bps - but trust me when I say they make the difference.
Giulini was well known for his taste for slow tempos, but here gets in my opinion just the right speed, which is comfortable for the singer and still not too diluted.
I'll briefly talk about other interpreters: Gösta Winbergh in the celebrated Karajan recording (Berliner Philharmoniker) sings with a good presence but a) orchestra's tuning is excessively high for my taste and b) he is often a little faster than the orchestra and has to correct himself, especially on long coloraturas.
Stuart Burrows (the conductor of this really good edition is Sir Colin Davis) sings well, but I feel like he's always risking to fall of the edge regarding pitch precision - he doesn't, or at least not too much, but I get that feeling.