While mezzo-sopranos typically sing secondary roles in operas, notable exceptions include the title role in Bizet's Carmen, Angelina (Cinderella) in Rossini's La Cenerentola, and Rosina in Rossini's Barber of Seville (all of which are also sung by sopranos and contraltos).
Many 19th-century French-language operas give the leading female role to mezzos, including Béatrice et Bénédict, La damnation de Faust, Don Quichotte, La favorite, Dom Sébastien, Charles VI, Mignon, Samson et Dalila, Les Troyens, and Werther, as well as Carmen.
[1] Some roles designated for lighter soubrette sopranos are sung by mezzo-sopranos, who often provide a fuller, more dramatic quality.
Usually men singing within the female range are called countertenors since there is a lighter more breathy tonal (falsetto) quality difference.
The roles they sing often demand not only the use of the lower register but also leaps into the upper tessitura with highly ornamented, rapid passages.
Although coloratura mezzo-sopranos have impressive and at times thrilling high notes, they are most comfortable singing in the middle of their range, rather than the top.
Rossini demanded similar qualities for his comic heroines, and Vivaldi wrote roles frequently for this voice as well.
[1] The dramatic mezzo-soprano can sing over an orchestra and chorus with ease and was often used in the 19th century opera, to portray older women, mothers, witches and evil characters.