To me Mr Mr the single is very week vocally ... the girls held back or it the way the song is suppose to be sung idk ... but it's some of the weakest vocals when compared to other dance numbers of SNSD Mr Taxi , Twinkle , Gee , Oh, The Boys all seemed to have the girls singing and taking command of those song ... this one didn't hook me with the vocals.
I believe that Girls' Generation's singles are relatively easy to sing in comparison with a few of their ballads, like "Lost in Love" or "Star Star Star." But I also believe that the vocals in Mr Mr are just as powerful and passionate as any of their title tracks.
*side note: I'm glad to see a FFIV fan on Soshified. Rydia is one of my favorite characters from the game because she was ridiculously powerful as an adult.