To be honest, I'd say it depends on a variety of factors. The medium, the characters, the dialogue and the story itself.
I have a short attention span and in terms of comics and novels, if I'm not reeled in by the first chapter, I'm already too bored to care. Even if the start is boring, if I look at the description or summary, and it bores me, I'm not even going to try. And there's also the cover. If the content was all it was to the medium, nobody would give a crap about well done posters or covers or ads. The covers and posters, trailers, etc., are the first things your potential reader/watcher is going to see and that is what is going to give them the first impression of your work. If it looks half-assed, they're going to think the content is the same if not worse and this is how my own mind works.
Now say I pick it up anyway even though the blurb left me yawning and the cover made me want to drop it. That first line in your comic or movie can set the mood of the reader like a snap. It needs to hook them, and the last line needs to make them want to read more. An example of this would be a comic on here know as Rock and Riot. It has so many things that appeal to its target market; great art, top notch dialogue, interesting characters, people in the minority group that they could relate with, etc. If I'm not hooked by the first line of the first chapter/episode to the last, and it's slow as heck, I'd probs drop it.
My exception to this would be the characters. Characters are my favorite part of any medium and if the person set them up well, I'd be curious to carry on and learn more, see how they grow and will probs get so attached to them I'd re-read/re-watch it again and again (This was me with the movies Paranorman, Spirited Away and Black Panther).
And uh...sorry about the long reply. I got too into it haha