Something blows you away when it is excellent. This thing can be a book, a movie, a show, etc. It can also be a personality trait that impresses you, such as someone's kindness, generosity or hospitality. It can be an excellent performance, as well, such as that of an athlete or an actor. So if you just watched a show, and you enjoyed it tremendously, you could say something like, "Wow. That completely blew me away."
A: Wow. That was an awesome movie.
B: It totally blew me away.
A: Kate Winslet was amazing.
B: That scene in the courtroom, I thought, was really gripping.
A: I know. Her performance there completely blew me away.
B: She totally deserved that Oscar.
Alright folks, think of the last thing that you read or saw or experienced that blew you away, then ask friends to tell you about the last movie or book that blew them away.