The two I know of actually have relevant experience to add to the reaction.

The first has done music and video production for years and will often critique MVs in those ways. He will talk about the colouring of a MV, for instance, and the lighting and editing as well as how the music works. He will often view the MV twice in the reaction video - the first time straight through with a few comments, and the second time he will pause it for more detailed comments.

The second has been studying classical music theory and musicianship and roped in a whole heap of fellow musicians to react to music. They comment on extraordinary details about the music, like unusual chords or voicing.

Reaction videos where fans simply gush over the latest video don't do anything for me.

Wade.

Professional choreographer assembled her list of difficult and very difficult dances and lauded why the artists who pulled it off did so so well. Gave me an insight into a couple of idols I hadn't really paid attention to.

Wade.