The cast of Signature’s “Showboat.”

Signature Theatre’s production of Showboat demonstrates two things: that sometimes a hefty dose of an old-school musical is just what you need, and that even those old chestnuts can still have some surprises in store.

Take Terry Burrell’s rendition of “Bill,” Jerome Kern and Oscar Hammerstein’s classic ode to inexplicable love (I remember the lyric, “I love him because he’s…I don’t know,” getting a half hour-long rave from my college music professor). Burrell’s chanteuse Julie sings this song through her whiskey, as she’s careening toward both career and personal ruin. Burrell here is defiant, knowingly heartbreaking. It’s as if she’ saying with each tremor, “This is the talent I have, and I’m more than determined to waste it.” It’s mesmerizing.

Largely, though, this Showboat is a production of more standard pleasures: a soaring orchestra, a powerhouse ensemble, and an epic scope. The adaptation of Edna Ferber’s novel (she also wrote Giant, of which Signature recently gave a sprawling musical treatment) packs a lot into two and a half hours, from interracial politics to disheartening tales of family abandonment, mostly set on the titular traveling ship. It also can be criticized for ending rather abruptly. Signature can do little to alleviate this quibble with the work, though it powerfully frames the show’s parting image, ending things on a note of hope.