What does it take for an intro to lose you?
Specifically for webcomics, I tend to drop stuff that give me the immediate vibe of "this was inspired and totally not derivative of the last three anime I watched". If it starts with a young man/boy who is totally average at everything and suddenly encounters a bright red/blue/green/etc.-haired girl with magical powers who drags him off to fulfil some kind of heroic purpose then I've pretty much conked out. If everyone has vaguely Japanese names and outfits that look like an edgy 13-year-old's ideal wardrobe then I'm out.
There are also series that feel like they were made just so the author can show off how subversive they are. If the series description is insert common storyline/trope here
BUT THE OPPOSITE HAPPENS DUN DUN DUN
that's a huge red flag for me and I tend to drop those comics early.
How long are you willing to wait for things to get interesting?
If the series gets some kind of reaction out of me every chapter then I guess forever
. I don't think emotional stake in an incomplete/abandoned series is a bad thing. Sure it might not feel good, but I don't ever think of it as a waste of time. With that being said, I also drop most comics/books within the first 10 pages so maybe that's really how long I'm willing to wait.
What makes you stick with one medium longer than the other?
I usually stick with books and movies for no reason than that there are more of them out there to choose from, and so more unique offerings. Comics are great too, but the time gap between finding excellent comics is usually way longer than finding excellent films/books for me. Books particularly stick in the head longer, for the reasons that OP already mentioned. You spent the time imagining everything and so you remember easily; with most blockbuster the visuals/sounds just do the thinking for you and I usually can only remember the direct series of events and nothing else (no nuanced emotions, etc.) upon leaving the theatre.
How long was the intro in your story?
Tbh going by the little amount of time I have to spend on it probably 7 years. 