Admittedly, the first part of the piece seemed dragging to me. It was too slow and we know how the tempo of Call Me Maybe is sung. But I stuck with it a little more until I reached the build up. Indeed, the strings supplied this building tempo and from then on, the music became spectacular. What's also nice about this video are the singers and artists themselves. If indeed given a chance to do a rendition of a very popular song, wouldn't the excitement simply get you carried away? But as I listened to it, the excitement was a good one. At least I think it didn't sacrifice the quality of the rendition.
Then again you may have your own opinion about it. It isn't easy to appreciate choral and/or orchestral music. But it is nice to give it a chance.