Useless art musings
The question of artistic merit of any piece can be reduced to: "does it (the piece) accomplish its goals?" If the goal of a youtube video is to reach a million views and it does not, or the author aspired to evoke some kind of emotion or action out of the viewer, one could say that the video failed and it lacks in merit. There are more sides to this though, and indeed one should not find any solace of objectiveness or fixedness or indeed any kind of reduction in complexity of the question. For, while indeed the term "goals" is vague, and many more well-read people have come up with indeces and categories of goals an author may have in creating, the real complixity lies concealed in the perspective. An author and a consumer often have different wants out of any a piece, and perhaps the question could be reframed to "does the artwork accomplish its goals for the person or perspective in question?", but this is a clumsy wording. Most often the perspectice in question is either you or your conversation partner, or the author. Did the artwork do for you what you wanted out of it when you decided to consume it, or alternatively, did the artwork do for the author what the author wanted out of it when they decided to make it? The true complexity of the question reveals itself.This does, however, allow us to clearly see the scope of the question. To ascertain the true absolute merit of an art piece is impossible, for it would requre is to know the way it affects every person who has interacted with it and will interact with it. We can assume when someone asks the question "is it good?" or "is it worth the watch?" about a media that they have the typical goal of media consumption, often a combination of a satisfying viewing experience (what that constitutes will not be discussed) and to be moved or affected or challenged in a way. There are more goals than these, however, but they usually remain unspoken. You can watch a movie mostly to have a good time with a friend, save a drawing only because a friend made it, or play a game for school, for practice, or for completion. These are all different goals (to have a good time, to have a memento of your friendship, to learn, etc.), but they are usually outside of the scope of the question "is it good?". This does not diminish the merit of the artwork itself, though. Additionally, a disagreement in the merit of an artwork can sometimes be explained by differing goals (as well as a difference in whether it achieved it). Perhaps you wanted to be challenged and your conversation partner simply wanted something to put on in the background.
One should also not make too strong of a disctinction in goals between author and consumer. Firstly it is impossible for an author to not also be a consumer themselves, because it is impossible to create art without experiencing it itself, nor to create art without emotion or thought about it. Secondly, the passive act of viewing also entails the creative act of interpretation (and perhaps there is no such thing as passive viewing after all, for viewing without interpretation simply does not exist).
Never does any person have just one reason or goal for art, but this does not have to be problematic per se, because it is possible to scope the question to your liking. Both the perspective and the goal can be made explicit in asking the question of merit. You can ask for whom, or why, or what the question is about. Without making it explicit, the normal goals from earlier will be implied, as the full question is too broad for any use.