Opéra Dialogué

Opéra dialogué was the style of opera promoted by the Kuchka in the 1860s and 1870s. The idea originated with Cesar Cui who felt that an ideal opera was an unchanged setting of a good literary text in a semi-melodic recitative style. The idea was to make the music blend with the speech of the characters as much as possible and to cut out all the "extra" music (arias etc...) which was unnecessary for the plot. Thus were to be no closed form musical numbers in an opéra dialogué unless a character in the drama was actually singing a song in the story or something like that.
One of the first composers to try an opéra dialogué was Dargomizhsky, who did The Sone Guest. Although it wasn't a hit with audiences, the Kuchka held it up as a standard for that they wanted in opera. Cui's own attempt, William Ratcliff was a complete failure and was treated brutally by critics. The general dissaproval of opéra dialogué was probably rooted in the fact that there was significantly less melodic material for the audience to hold on to, and no virtuosic arias or such things that they commonly appreciated.
Musorgsky also started work on an opera dialogue project, The Marraige, on a text by Gogol. In so doing, he developed his skill of writing speech-like musical settings of the Russian language. He made the musical line follow the pace and cadence of speech. This meant that odd angular intervals were used in the melodic line and strong syllables were placed on strong beats where they would sound natural--agogic accents and the like.
Musorgsky only finished one scene of The Marraige, realized it would not succeed, and moved on to a new operatic project, Boris Godunov. But he applied much of this new technique to his initial version of Boris.