This medley by acapella sensations Pentatonix blew me away. The singers are fabulous, that much you'll see within about 10 seconds of the start of the video. The arrangement is also stellar. They had to make decisions about when to cut from one song to another, and in their choices they made it as smooth as can be. At the end of the video they give a very genuine thank you and a little apology in case they left out your favorite song...very cool!