Irving Berlins holiday perennial features an amazing cast, singing and dancing at the top of their game. Each new set is a meticulously wrapped Christmas gift guaranteed to thrill and delight upon opening; and impeccable, colorful costumes abound. Likewise, the score is fruitcake dense, chock full of classic songs; and the orchestra will whisk you away on gossamer wings of Christmas nostalgia. Trouble is, beneath the tinsel, theres no there there. No plot that has a genuine connection with Christmas, no reference to the Nativity, peace on Earth, goodwill toward men, or even some vague generic nod to the reason for the season. Its a big, buoyant, vapid Xmas card that, while set mostly in the 1950s, might just as well have been called Irving Berlins Festivus for the Rest of Us. On the upside, you get plenty for your money: song and dance until youve had your fill; great ensemble showcases (Snow, Ive Got My Love to Keep Me Warm); immortal show tunes (Happy Holidays, Blue Skies, and White Christmas); and solo show-stoppers, including Let Me Sing and Im Happy and How Deep Is the Ocean. KEVIN PHINNEY [See Kevin's full review.] (7:30 p.m. Tues.-Wed. and Mon., Dec. 21 & 28; 8 p.m. Thurs.-Fri.; 2 & 8 p.m. Sat.; 1:30 & 7 p.m. Sun. Ends Dec. 30.).