"Well, basically there are two sorts of operas. There's your heavy opera, where basically people sing foreign and it goes like 'Oh oh oh, I am dyin', oh, I am dyin', oh, oh, oh, that's what I'm doin', and there's your light opera, where they sing in foreign and it basically goes 'Beer! Beer! Beer! Beer! I like to drink lots of beer!' although sometimes they drink champagne instead. That's basically all of opera, really."
Opera has been around since the end of the 16th century and still going strong. Major opera composers include Mozart, Handel, Verdi, Gioachino Rossini, Wagner, Puccini and Richard Strauss, though there are, of course, many more.
The public perception of the difference between opera and The Musical is that musical theatre has breaks for spoken dialogue, whereas opera is "sung through", alternating between "arias" (big numbers) and "recitative" (music written in the style and rhythm of dialogue). While not a bad approximation, it's also not true. A number of musicals are sung straight through, such as Les Misérables and Joseph And The Amazing Technicolor Dreamcoat, or nearly so, like The Phantom of the Opera and RENT (the latter in fact uses dialogue explicitly for Wham Lines!). Likewise, several opera, like The Magic Flute and Carmen, involve spoken dialogue. The actual line between musicals and opera is blurry and kind of technical, but the short of it is that opera doesn't use electronic sound equipment and musicals typically need better actors than singers. Stephen Sondheim was heard to claim, "I really think that when something plays Broadway it's a musical, and when it plays in an opera house it's opera. That's it."
The public perception of opera is that it's always a tragedy. This is also not true; the opera genre is as varied as any other. Many operas are comedies, and even the serious ones tend to have at least some humorous parts. And while some operas have incredibly well-crafted lyrics and story lines that are true works of art, others are... not quite as brilliant.
That said, the opera genre is known for featuring many a work with extremely drawn-out texts focusing on a single (often trivial) theme. As a result, opera texts (libretti) are often mocked, and in many cases it's mainly the quality of the music that makes an opera work, along with the same thing you need for any theatrical production: committed performers bringing the art form to life on stage. Movies have car chases, rock songs have guitar solos, and operas have death-arias (the soprano frequently dies). In fact, both Anna Russell and B.J. Ward (in her one-woman show, Stand-Up Opera) have made entire comedy routines of poking fun at opera tropes.
Nowadays we tend to think of operas as high-falutin' fare for the nobs and snobs. Back in the 18th, 19th, and early 20th centuries, though, opera was popular music, to the point that the opening night audience was chock-full of transcriptionists. And it didn't take long for them to produce a saleable product: Rossini once said that by the time he left the opera house for home at the end of opening night, hawkers would be lined up on the street selling copies of the music and lyrics of his arias to those who couldn't afford a ticket.
Several modern films and other works have been created as operas (that is, entirely consisting of sung dialogue). The most famous "serious" opera film is probably The Umbrellas of Cherbourg, starring Catherine Deneuve. A very modern example is Repo! The Genetic Opera, which transplants the style into industrial sci-fi horror. The term Rock Opera is thrown around at times for a sub-genre of the themed Concept Album, but most "rock operas" are not produced for the stage (with an exception or two). The nearest thing to a modern successor to opera is Broadway-style Musical Theater. Indeed, musicals can trace their origins to opera through the operatic subgenre of operetta or light opera, which, as its name implies, is light in terms of subject matter (i.e. it's funny) and music, and often feature a good deal more plain dialogue than ordinary operas. The works of Gilbert and Sullivan are generally considered transitional, as while they considered their works to be comic operas, they would probably be called musicals if produced today.
Used in movies and TV shows to add a touch of class. Or just something artsy. Or for the cast to get bored and fall asleep, which is something that can't be done (too loud).
Not to be confused with the Cantata, though at least one cantata, Johann Sebastian Bach's Coffee Cantata, can be considered a miniature comic opera according to The Other Wiki.
All There in the Manual Without a program, good luck trying to understand what's going on on stage. Many modern opera houses (Especially in Germany) show the text right above the stage, and some fancy opera houses even have a small screen on the back of the seats with the text in several selectable languages. Performing opera in translation has disadvantages too. It's often just as hard to make out the words, and when you can the effect isn't always what it might be. For example, to an English ear Tosca (in one of the rare operas with a stonking good story) may sound dramatic when she sings 'Mori! Mori! Mori! ... È morto.' but translated into English this becomes 'Die! Die! Die! ... He's dead.' 'Nuff said.
All Musicals Are Adaptations: Opera gets this from both sides. Many operas are adaptations of existing works, and a number have been adapted into modern musicals.
Brawn Hilda: A rather unfortunate stereotype of opera singers (as in the saying, "It ain't over till the fat lady sings"). Although it's usually very exaggerated, it does have a degree of Truth in Television since the vocal pipes necessary to support a huge operatic voice often go along with a larger frame. The trope may have originated from Wagner's Die Walküre, where the main character, Brünnhilde, is often played by an imposing woman. Though if you think that means opera singers are unattractive, think again.
Creator Couple: Practically every opera by Vincenzo Bellini that you will see (except his last, I Puritani) has a libretto by Felice Romani.
Crosscast Role: There are many "trouser roles" for women playing men and several "skirt roles" for men playing women. In the Baroque period (Opera's earliest century-and-a-half), female roles were often played by male castrati. (And, yes, a castrato is exactly what you think it is.)
Dawson Casting: Due to the physical requirements and amount of training involved, teenage characters like Cio-Cio-San (Madama Butterfly) or Salome are almost always portrayed by singers in their twenties or older. And teenage boys are generally played by adult women, usually mezzo-sopranos. Sometimes averted with less demanding roles such as Barbarina from The Marriage of Figaro, who is occasionally played by a high-school aged singer.
Everyone Is Jesus in Purgatory: Individual operas may very well be subject to this, but the entire form of Opera is actually a product of this. In attempting to revive classical Greek plays to the theatre of the Renaissance era, interested scholars decided that the Greek plays were meant to be sung in their entirety. New works followed suit, and the rest is history.
David Merrill: You're the rat again, aren't you, Daddy?
Robert Merrill, baritone: The baritone is always the rat, my boy.
Farce: The plot of many comic operas. There's even a whole genre called "opera buffa" (to distinguish it from "opera seria"). Notable examples are The Marriage of Figaro, The Barber of Seville, and L'elisir d'amore, all of which are screamingly funny provided the cast is on their toes.
Femme Fatale: All the best diva roles. Special mention goes to Violetta from La Traviata.
Flame War: For all the veneer of civilisation in the genre, opera enthusiasts can get just as vicious in defense of their favourite singers and composers as any other fans. Just go have a look at the comments on any opera clip on YouTube.
Incredibly Long Note: This and this, for starters. In fact, some famous singers like Birgit Nilsson & Franco Corelli made it a friendly sport over who'd black out first from holding that high C in Turandot. Everyone else peed in excitement, of course. Expect this trope (especially of the soft-but-incredibly-held-out variety) when you see Montserrat Caballé on the cast list or album notes.
Large Ham: Opera has long been full of hammy divas and divos (many roles, and perhaps the very nature of Romantic opera, lend themselves to this), though singers and productions seem to be averting this trope more and more these days, partly thanks to speakers making it no longer necessary to have No Indoor Voice.
Leitmotif: Wagner Wagner commentator Hans von Wolzogen is the Trope Namer, although the concept predated Wagner by quite a while
Love It or Hate It: Richard Wagner. Composer of the finest music and producer of the best plots ever, or overly bombastic and just too damn long-winded? One of the less intelligent criticisms of Wagner is that he was "Hitler's favorite composer". This is kind of unfair; Wagner couldn't possibly have pandered to Hitler in any way, since he died before Hitler was even born. (And of course, Hitler Ate Sugar.)
Melismatic Vocals: Or 'coloratura'. Bread-and-butter for ALL voice, but ideally for belcanto roles. A huge plus if you have a large voice (dramatic coloratura) - although having a large voice and a dramatic voice is not necessarily the same thing.
Lampshaded gloriously in most Baroque operas. Expect the vocal line to fall when singing about sadness or despair; rise up when singing about glory, anger and war; have crazy roulades when singing about being in love (as in "adrift in a sea of love").
Power Echoes: The Valkyries from Die Walküre were originally conceived as singing their entrance war-cry off-stage into actual megaphones ('singing trumpets'). Played straight in Siegfried with the dragon.
Recycled Script: Several examples, but Rossini was particularly well known for lifting music from one of his operas to another. It was acceptable at the time, as long as the two works didn't premiere in the same town.
Rule of Drama: The meeting of the queens in Donizetti's Maria Stuarda, just to name one example.
Rule of Three: Many operas have three acts, especially those of Wagner. For Verdi and Puccini, their third operas (respectively with Nabucco and Manon Lescaut) formally launched their careers.
Satellite Love Interest: Very common - as in the Commedia dell'Arte, viewers are given little explanation as to who the inamorati actually are. They're young and in love, which usually sums up both characters' entire personalities (or at least the soprano's).
Tear Jerker: Some operas, especially ones by Puccini, seem engineered specifically to be as heart-rending as possible.
That Makes Me Feel Angry: In opera, this trope is pretty much a must-have, since the music is more important than the words and many singers don't bother acting things out too much. Opera is full of (insert adjective here) mi sento and other status-descriptions. Or the composer/librettist put it in to give the singer an indication of how the character should feel; singers are expected to act nowadays. Also, during the Baroque era, musical drama tended to be structured according to the so-called doctrine of affects, with consecutive numbers depicting contrasting emotions - a lilting love duet followed by a furious vengeance aria, for instance. If the idea is to juxtapose readily identifiable emotions for maximum effect, it makes sense to flag them in the libretto.
Willing Suspension of Disbelief: Pretty much a given for all operas ever. Many plots are completely implausible, The Casanova is often played by a short, fat, middle aged guy, The Ingenue is often played by a tall, buxom woman, and there's only so much costuming can do. Opera is pretty much built on this trope - generally, the audience is there for the music.
It also creates a certain amount of Colorblind Casting, since the voices are usually cast indiscriminately of the singer's race.
Gilligan's Island: Cast creates in "The Producer" episode an operatic rendition of William Shakespeare's Hamlet, set to the Habanera and Toréador melodies from Carmen and the Barcarolle from The Tales of Hoffmann).
Heavenly Creatures: Toward the end, just before the tragic finale, Juliet stands on her balcony and sings "Sono andati" (Are they gone?) from La Boheme. It's actually Kate Winslet singing. On the fatal walk, the Humming Chorus from Madama Butterfly is heard. It creates an unbearable dramatic tension, especially if you know the story.
The Donizetti Queens refer to three of his dramatic operas: "Anna Bolena" (Anne Boleyn), "Maria Stuarda" (Queen Mary Stuart), and "Roberto Devereux" (Queen Elizabeth I). Apparently the main characters for all three are very hard to cast, and it's considered major achievement to sing all three.
L'incoronazione di Poppea (The Coronation of Poppaea)
L'Orfeo (oldest opera still regularly performed) (The Trope Maker)
When Monteverdi composed L'Orfeo, Opera as a genre didn't yet exist. The collection of songs to be performed back-to-back was merely advertised as Monteverdi's new "works." The Latin word for works is opera (plural of opus), and the term has been with us ever since.
Il ritorno d'Ulisse in patria (The Return of Ulysses to his Homeland)
Turandot (suffered Author Existence Failure. As conductor Toscanini put it partway through the final act on opening night, "Qui finisce l'opera, perché a questo punto il maestro è morto," or, "Here the opera ends, because at this point the maestro died." You've heard "Nessun dorma.")
Witnesses later said Toscanini's words were "Qui, il maestro finí", here the maestro finished, which is more consistent with Toscanini's brusque personality.
Dido and Aeneas (the most well-known pre-20th-century opera written in English)