My opinion: It was alright.
At first when i found out i had to do the musicals, i was like, omg no way this is soo dumb! but then i started playing, and i had a lotta fun! haha. me and my friend were like on the floor laughing. I liked all of the songs, and like others have said, it was nice to have a break from the constant button mashing. I've never had anything against Atlantica, i enjoyed it in the first games, and in the second. I wish in the second there was some action, but i definatley had fun with teh musicals! I sang along! ( it's okay, admit it, you did too).
It was like totally embarassing playing those parts though, like my brother who's like 17 was watching me play, and he's like "wtf is this game? I thought you said it was sorta like FF?" erm, yeah.
To get to the point, the Atlantica were funny/entertaining/ a little embarassing/refreshing/ a little dissapointing.