The afternoon show was almost sold out (the evening show was sold out) and it was an unusual experience, while waiting to enter, to be surrounded by 2,900 people who were all able to pronounce the word "Celtic" correctly. The audience, interestingly enough, skewed heavily female.
The show started on the dot, and the next two and a half hours were a continuous burst of energy. All of the performers are powerful singers and some of the songs were quite emotional, notably "Isle of Hope / Isle of Tears" about the Irish emigrants to America. There was a mix of traditional and popular songs, more than thirty in all, plus two instrumental numbers with stunning dancing. The show finished up with a rousing performance of the patriotic "Ireland's Call", with all six singers in formal kilts, and the audience responded with a standing ovation.
Here are a couple of videos to give you a sense of the flavor of Celtic Thunder's shows:
See also "Heartland", unfortunately not performed in the current tour -- perhaps out of concern that Americans wouldn't relate to singing in Gaelic?
Celtic Thunder's tour page is here; they're in our country through December 17. If they're performing anywhere near you, the show's well worth checking out.