We know, because we have over 100 years of recordings, that classical music technique has greatly improved over time. Ability and polish that we take for granted today was once unheard of. And orchestral performance is amazingly improved. Orchestras today play much familiar music, but in the past, most music was given few performances by musicians totally unfamilar with it.
In modern rehearsals, the conductor can direct the orchestra to start at "letter D" or at "measure 140", and everyone can start playing some difficult passage together. Rehearsal letters and measure numbering is a relatively recent invention. In Beethoven's time, there was no easy way to start everyone together in the middle, making rehearsal of any kind problematic. Which brings us, finally, to the Opera Carmen.
Bizet's opera, whose music is still so fresh and wonderful today, flopped miserably in its first two runs. Anytime you find yourself enjoying Carmen, ask yourself how those first French audiences failed to catch on to it.
Now it's true that the plot was shocking for its time. And the French were not used to such vigorous music. And maybe it opened in the wrong venue - the Opera Comique - a place for familiy-oriented entertainment. And a lot of the Carmen we enjoy was not present in the first runs. The "recitatives" that string the big numbers together, where a lot of the plot is gently and beautifully sung, were not composed by Bizet, but added later by a friend, Ernest Guiraud. At first those parts were merely spoken. (Today the use of this added music is somewhat controversial. See the wikpedia for lots more fascinating info about the first performances.)
But even after taking all that into account, I'm sure of one thing: those initial perfomances must have been awful. Really awful. I imagine rhythms obscured by instruments playing off the beat; thousands of wrong notes; hundreds of missed entrances; feeble sounds from timid singers. If you ever have a chance to attend, say, a middle school perfomance of Carmen, you'll probably be hearing something a lot better than was heard at the Opera Comique in 1875. Gosh, it must have been really, really bad.