What makes a good yoga video? Here are my criteria:
Instruction is clear, to the point, generally nontechnical. Humor is also appreciated (though video instructors generally are a very serious group).
Postures are appropriate for the targeted student level. If the video is directed to both beginners and more experienced students, then there should be demonstrations of variations appropriate for the different levels.
Teacher and any models are comfortable in front of a camera and demonstrate the postures with ease and grace.
Sequence of the postures is logically arranged.
Props. I know that many yoga schools don't use props. I understand, too, why props are difficult to include in a video. But I can't help it: My experience as a student (for 19 years) and a teacher (for 12) has convinced me that props are important, especially for beginners. So I look for how the teacher uses props (if at all), especially in Shoulderstand.
The setting of the program, while it should provide a pleasant environment for the instruction, is secondary to the above criteria. Some videos are filmed on elaborate sets or in exotic locales, which is fine, but I'd never recommend a video just because its backdrop is a beach in Hawaii. Some of the best videos I've seen were made in a small studio or on somebody's backyard deck.