Four Brony reactors' reaction to "Smile HD" rolled together.
Reactor names are listed onscreen on their respective sections and the channel links are listed below.
Bottom Right: https://www.youtube.com/user/Mastermax888
Bottom Left: https://www.youtube.com/user/Bronymonster44
Top Right: https://www.youtube.com/user/mlpwarrior1302
Top Left: https://www.youtube.com/user/ratchetness

Smile HD: https://www.youtube.com/watch?v=PqVVtaWd8Pw