FOXBORO - Pleasant. And pleasantly surprised. That's what I was after imbibing Bay Colony's very fine version of Shakespeare's gender-bending staple "Twelfth Night" last weekend.

Bravo and brava.

As told previously, I'm not a big fan of amateur Americans tackling Shakespeare, as difficult as it is on modern ears, written in an archaic cadence and diction meant to be tripped from tongues who wag the King's English. Having seen Bay Colony's uneven "Macbeth" last season, with various actor diction all over the Scottish map, I had no better expectations for this year's offering.

I was wrong.

Thanks to two strong newcomers to the Foxboro stage - and several troupe members who are winning in every show they tackle - this 407-year-old comedy of mistaken sexual identity, disguises, mischief and more, which has shaped every gender-bender story to follow, is a delight for the eye and the ear. For the uninitiated, "Twelfth Night," or "What You Will," involves identical fraternal twins (don't ask) Sebastian and his headstrong sister Viola, who have been separated and presumed drowned after a vicious storm at sea. Viola washes up on Illyria, disguises herself as a boy, assumes the name Cesario, and becomes servant page to the Duke Orsino. Orsino is in love with the grieving Olivia, who spurns his many advances. On his behalf, Orsino sends his youthful page to woo Olivia, but the countess, intrigued by the impudent "boy," falls in love with "him," beginning a series of calculated and accidental misadventures which have warmed audiences' hearts for five centuries.

"Twelfth Night" is always about heartfelt performances. Poor ones make it impossible for an audience to suspend their disbelief to accept male and female actors as twins so alike "as to confuse the senses."

However, thanks to those newcomers, this show works. Erin Thomas makes for an enthusiastic, if Chaplinesque, Viola - although she could use more bearing and passion in her entreaties, especially in the climactic, final "great reveal" scene. Bay Colony newcomer #2, Marco Zanelli, is terrific as the smitten steward Malvolio, the ill-used servant who is duped into thinking Olivia worships him. Zanelli's diction is a clinic in how Americans should enunciate the cadences of 1601 London. Returning performers who shine include Attleboro's David DaCosta as the Duke. DaCosta, the best reason to see "Macbeth" last season and superb as the Beast in February, has whipped himself into fantastic shape and glows here, albeit in a lesser role. Michael Warner, also always good, whether playing the hick Willard in "Footloose" or George Bailey in "It's a Wonderful Life," is a beacon as Viola's twin Sebastian, although he and Thomas really don't look alike at all. Ray O'Hare - a cross between Charlie Chaplin and Bill Irwin - plays the Tramp-like fool with aplomb. The stunning Carol Kautshire, all sharp eyes, carriage and attitude as Olivia, has little trouble making you believe she is desired by several dashing men.

In the show's completely buffoonish subplot - which Shakespeare wrote exclusively as lowbrow humor for poor, simple theater-goers in the Globe's ha-penny seats - MB Murphy as Sir Toby Belch, Viola's uncle, is a wonderful walrus-like foil to Daniel Kozar's fey, foppish Sir Andrew Aguecheek, a foolish suitor of no good means.

Murphy, a woman in a role written for a man, adds a gender-bending element even Shakespeare hadn't intended, but just a few minutes into her first scene, she's got you under her believable spell as the drunken, ne'er-do-well instigator. Kozar, a tower of hissing, strutting nonsense, is a hoot. Rehoboth 8th-grader Michael Salhany shows a maturity beyond his years and great acting potential as the servant Fabian. Craig Lampert as Sebastian's savior and friend, Antonio, adds a sensitive element in the caring role of protector. Director Steve Dooner, who keeps the action humming along with appropriate zip and pace, further adds to the sexual confusion by having Antonio be openly in love with Sebastian (a fascinating issue Shakesperian scholars have long debated). Antonio is further wounded when his charge rejects him for heterosexual conformity.

You have to have solid legs to run on stages for five centuries. Such simple ideas - once the bedrock of theater - can seem old and overdone in this cynical age. But "Twelfth Night" endures and will endure for another good century, at least, and productions like Bay Colony's show you why.

"TWELFTH NIGHT" runs through March 23 at the Orpheum Theatre, 1 School St., Foxboro. Call 508-543-ARTS for ticket reservations.