It has to be said: Much of Riverdance is profoundly dumb.

This is not the fault of the performers — appealing, energetic, and superbly trained dancers, singers, and musicians who, on Friday night, inaugurated the local leg of their "farewell tour" at the Merriam Theater. Rather, it is because composer Bill Whelan, producer Moya Doherty, and director John McColgan have tried to tie together a group of unrelated numbers through an incoherent "theme" (something about sun worship and immigration) and an overearnest, prerecorded narration.

Individual parts of this staggeringly successful show, in its 17th year, were quite wonderful. These included: a powerful, rhythmically complex Irish step-dance performed by eight men; a pair of African American tap dancers who challenged each other to ever-greater technical and stylistic heights; the fine work of principal male dancer James Greenan; and anything featuring Niamh Ni Charra, a virtuoso on fiddle and concertina.

But other aspects of Riverdance were less successful. For there was way too much stage smoke (a.k.a. Irish "mist"), which only managed to obscure the lovely and intricate footwork of the main female dancer, Alana Mallon. Riverdance's designated flamenco dancer, Marita Martinez-Rey (who, like all the artists, boasts a stellar resumé), was appropriately proud and fiery. But it was a mistake to add four male Irish dancers to her initial piece. Dressed in silvery, spacemanlike outfits, they seemed to have wandered into the wrong theater. Also, the "Irish" singing — of which there was a great deal — sounded too New Age, and a lament about slavery seemed completely out of place.

Still, the vast majority of the opening-night crowd clearly adored Riverdance, which has long been immune to negative reviews. It is a true cultural phenomenon — inspiring several spin-offs and numerous parodies; playing to sold-out houses all over the globe; and providing good jobs for countless young performers. Some people even credit Riverdance with helping to spark the recent renaissance in traditional Irish culture, including the Irish language.

The basic idea of putting several other kinds of percussive dancers onstage alongside traditional Irish performers is good. But it would be even better if its creators hadn't tried so hard to make it "mean" something.