My grandson wrote to me from the USA, and mentioned that he and his girl friend had tickets to see Aida. I had just finished teaching a course on that opera, it was all fresh in my mind, and I didn't see why he shouldn't have the benefit of my wisdom. So I sent him the following:

When the Suez Canal was almost finished, the Khedive of Egypt decided that the festive opening should include a grand opera to be performed in the grand opera house in Cairo. Wanting nothing but the best, he solicited Verdi. But Verdi had retired several years before, rich and famous, and at first was not interested. The Khedive insisted, and gave him the text to read. What aroused Verdi's enthusiasm was partly the local color, but mainly the drama.

The three central characters constitute a conventional love triangle. But their suffering, in all three cases, is the struggle between their uncontrollable desires and the duty that society imposes upon them. The star-crossed lovers are Radames, general of the Egyptian army in the war against Ethiopia, and Aida, daughter of the Ethiopian king, now a captive and the slave-girl of Pharaoh's daughter. Amneris, Pharaoh's daughter, is also madly in love with Radames, and therefore jealous of Aida. Aida's father the Ethiopian king (also a captive) forces her, in spite of her love, to worm a military secret out of Radames. Radames, because of his love for her, allows himself to be tricked into revealing the secret. Amneris, in spite of her love for him, hands him over to the merciless priests who condemn him to death. All three are doomed from the beginning, as their personal feelings bring upon them the cruel punishments of society.

But there was also the attraction of the local color. Since the opera was to be part of festivities in Cairo, the story is set in ancient Egypt. Verdi's local color is colorful, but hardly authentic. The wonderful triumph scene (Act 2 Scene 2) is actually modeled on the triumphs awarded victorious generals in ancient Rome. Verdi insisted on having straight trumpets (ever since called "Aida trumpets") specially made to play the march on stage, but they are copied from Titus's Arch in Rome and so probably resemble the trumpets used in the Temple in Jerusalem. Of course, nobody knows how the music of ancient Egypt sounded, so Verdi made do with the fake Arabic style that passed for "exotic" at that time.
(Example: chorus and dance of the priestesses at the beginning of Act 1 Scene 2.)

Verdi never stopped changing and innovating. He re-invented himself at least three times in the course of his life. The first new departure was Rigoletto, when he was 38 years old. After 15 successful operas, he changed his style: the music is no longer chopped up into discrete "numbers" but the sections flow one into the other uninterruptedly. Aida, composed at the age of 58, is again in a new and much more complex style. And his last opera, Falstaff, composed when he was 80, is again nothing like anything that came before.

The new style of Aida is more flamboyant, more spectacular than his previous works. But it is also a nationalist, patriotic statement: Italian opera's answer to the challenge of Wagner's. Wagner used musical labels, called Leitmotive (leading motives, because they direct the attention of the listener), that refer to persons or things or ideas in the drama. The orchestra does not merely accompany the singers, but plays independent music, the themes of which are these motives. The result is very sophisticated, but very dense and slow-moving -- very German. In Aida, there are several prominent leading motives which reappear throughout the opera at the relevant moments, but Verdi did not allow them to take over the whole, nor to destroy the directness of beautiful melodies that makes the opera so popular and enjoyable. So Aida, even with its leading motives, is very Italian -- very un-German.

The main motives are as follows: 
     Aida: delicate and introverted melody (symbolizing the helplessness of the lone woman in the face of the remorselessness of the world).
(Examples: the first theme of the orchestral prelude, her first entrance in Act 1 Scene1.)
     Priests: like a slow march (symbolizing the merciless character of the establishment). (Examples: the second theme of the orchestral prelude, the first thing the priests sing in Act 2 Scene 2: "Della vittoria...") 
     Amneris: a serpentine melody (symbolizing her devious character).
(Example: her first entrance in Act 1 Scene1.) 
     Amneris's Jealousy: hurried, nervous melody (symbolizing her suppressed rage).
(Example: during her dialog with Radames in Act 1 the words "Oh, guai se un altro amore...")

Thus, the style in Aida alternates between a sophisticated, complex mode (actually somewhat Wagnerian) and a simple, direct, attractive, popular mode. In the complex mode, the singers sing a prose text which is more recitative than melodic, while the orchestra plays independent coherent music, often based on the leading motives.
(Example: in Act 4 Scene 2, just before the final duet "O terra addio" there is a short dialogue between Aida and Radames while in the background the priestesses sing their prayer.)

In the popular mode, the text is poetic, the singers sing beautiful melodies with many repetitions, and the orchestra is limited to an accompaniment.
(Example: the first thing Aida sings at the beginning of Act 3: "O patria mia...")

In the first few minutes of the opera, Verdi displays this whole bag of tricks. The orchestral prelude begins with the Aida motive, symbolizing the lone helpless individual, played in high notes and beginning with four ascending notes. This is immediately followed by the Priests motive, symbolizing the merciless establishment, played in low notes and beginning with four descending notes. This leads to a climax, in which these two motives are heard simultaneously, symbolizing the contest between them. Then the curtain rises, revealing Radames conversing with the high priest. Their dialog is a perfect example of the complex mode, with a lovely repeated melody in the orchestra and recitative in the voices. Then the high priest leaves, and Radames sings one of the "hits" of the opera: the aria "Celeste Aida" ending with a long high note meant to stop the show as the audience applauds and shouts "Bravo!".

Another thing: In his later works, Verdi gave the main characters dramatic monologues, besides the arias with beautiful melodies and opportunities to show off their voices. As he himself admitted, these monologues are meant to be like the soliloquies in Shakespeare's plays.
(Examples: Aida's monologue at the end of Act 1 Scene 1: "Ritorna vincitor...," Amneris's monologue at the beginning of Act 4 Scene 1.)

Yet another thing: In his later works, the choruses that conclude scenes are cumulative. That is: you hear each of the components separately, and only then are they combined in a grand finale.
(Examples: in Act i Scene 1, this process begins with the King of Egypt singing an aria beginning with the words "Su del Nilo..." Then the priests sing a different melody, and then these two are combined in a chorus. Then the three soloists express their private thoughts, first Aida and Radames together, then Amneris alone, and then all of the above are combined in one monster chorus,
All of Act 2 Scene 2 (the triumph) works like this. It begins with the populace, then the priests. After the march and the ballet, there is a chorus combining both of these. Then there is conversation between the soloists, ending in an ensemble where everything they have sung is combined. Then there is more conversation, and then the scene ends with a monster chorus combining all of the above.)

My grandson wrote back, thanking me, but explaining that their tickets were for the rock musical Aida with music by Elton John. O tempora! O mores!