I'm not Cathe but have been working in the fitness field for a long time.
A fitness video critic should have a strong background in the areas of exercise phyisiology and kinesiology. A lot of what we see in videos isn't always good for us but the layperson would not know unless he or she knew what to look for. The more education I gain in this field the more upset I become watching videos that have risky exercises, exercises that do not target the muscle group being worked, led by instructors with little knowledge of even basic exercise physiology or kinesiology. Case in point: Doing chest presses with dummbbells while sitting up. A very well known video production company put these on their recent upper body tape. I grab my medicine ball and do chest squeezes in place of this. Would you be able to tell if an exercise does not effectively work a particular muscle group? Would you be able to evaluate an exercise and note that it might be risky for certain populations? Would you be able to suggest appropriate modifications for contraindicated exercises? Would you be able to determine if a particular routine made sense? The flow of a class is very important as well as the combination of exercises chosen to accomplish the goal of the video.
Critiquing videos goes way beyond judging for proper cuing, physical attributes, the intensity factor, etc. If you are really interested in pursuing this, my suggestion would be to further your education and learn about muscles and their joint actions, physiology, anatomy, and perhaps even obtain some certicications in the field.
Regards,
Roe