I feel like Les Mis and Scarlet Pimpernel really aren't that similar (though they are my two favorite musicals), because Les Mis is continuous music with more recitative, and every song in Scarlet Pimpernel has a traditional beginning, middle, and end, so the melodic structure is a bit different. The songs in Scarlet Pimpernel usually tell feelings or 'moments,' while Les Mis tells the story, as there is no dialogue to explain what's going on.
Les Mis also stays pretty consistent in style-- the songs flow into each other musically AND thematically-- while Scarlet Pimpernel uses very different styles-- "You Are My Home," "Prayer," "Creation of Man," "When I Look At You," "Falcon In The Dive," and "Where's the Girl," all sound like they come from totally different shows.
In my pants, she has burst like the music of angels, the light of the sun! --Marius Pantsmercy