Following last season’s grand Norma, the Chautauqua Opera Company achieved even finer results Saturday evening with a fine but under-appreciated Giuseppe Verdi work that represents a midpoint between the bel canto style of Norma and the full-out “music drama” Verdi and Wagner were to develop later in the 19th century: 1849’s Luisa Miller. While, it’s never been a crowd-pleaser like Rigoletto or La traviata, it’s a passionate story — full of melodrama, but also full of feeling — and the music is wonderful, culminating in a third act that ranks among the great single acts in Verdi’s huge output.