How can something so easygoing excite such polarized reactions?

Rossini's La Donna del Lago, the Metropolitan Opera's Saturday simulcast in six area theaters, has stars (Joyce DiDonato and Juan Diego Flórez), attractive melodies, a plot line borrowed from Walter Scott (The Lady of the Lake) plus a theatrical and musical sheen at every turn.

In fact, the 12:55 p.m. simulcast is a landmark of sorts for hardcore Rossinians, the apotheosis of a hugely influential 1819 opera that fell into deep obscurity from about 1860 until 1958. La Scala's 1992 outing signified a decisive arrival - directed by filmmaker Werner Herzog and conducted by Riccardo Muti. For some, it's a lyrical feast.

Yet others encountering the current Santa Fe Opera co-production are baffled by such advocacy, not to mention a prime slot at the Metropolitan Opera. The morning after the Feb. 16 opening, you'd recognize opera denizens on the street muttering, in passing, "no characters, no good tunes, can't hold a candle to William Tell."

I agree. Rossini's second-tier operas divide audiences not unlike fans of the Swedish pop group ABBA: The music is light, bouncy and enjoyable. Smart people like it and those who don't can only conclude that they didn't get that gene. The innovations represented by La Donna del Lago's were long ago overtaken, whether the dramatic integration of the orchestral prelude (not a typical overture) and the source material's Scottish gothic setting.

The handsome production by Paul Curran (whose La Traviata will be imported by Opera Philadelphia next season) has a lot of wide open spaces with foreboding skies suggesting the long-ago countryside of Scotland as well as hut-like interiors and, near the end, a red rectangle that focuses a narrative that needs it.

Whatever one thinks of the plot about warring clans and the heroine Elena (who could change the power axis with her choice among three possible suitors), the storytelling style has an early-19th-century formality and not the kind of musical variety that projects great character differentiation. Curran's direction often embraces that formality to good effect, while other moments try to pretend the narrative is more naturalistic; that doesn't hold up.

When you're captivated by the singers - which is likely when DiDonato and Flórez are on hand - such problems matter much less, even for those who didn't get the La Donna del Lago gene. In their absence, you wish conductor Michele Mariotti would take a stronger hand with the music or that Daniela Barcellona (in the trouser role of Malcolm) and John Osborn (as Rodrigo) had more vocal charisma.

The big picture, though, is that Rossini performance manner is evolving in the right direction. Voices generally are smaller, more fleet and less likely to turn the music into a laborious series of more emphatically punched notes. Subscribers to the entire season who aren't sure where their operatic genetics lie are encouraged to try at least one act of it. If the ticket is already paid for, whether for Saturday or the 6:30 p.m. Wednesday (March 18) encore, there's always the simulcast's star power.

Information: www.metopera.org or 212-362-6000.