Reaction videos are okay if they 1. Bring something interesting to the table in terms of discussion and insight into the topic being discussed or the content reacted to, and 2. Actually show respect for the source material they are watching and comply with fair use doctrine. But there's a crap tonne of content which is just people taking popular videos, playing them wholesale while bringing the odd fatuous comment to the table once every 5 minutes. Can't stand the latter type.