If I'm still interested after reading three strips, the comic isn't shit. If I'm still interested after twenty strips, it's
good.
A
great comic has to be consistently good. This includes both the quality of art and writing. Only one of the two is not enough. The art may be what will first catch my eye, but it is the writing and characters that keep me reading.
Funny strips have to be original or at least well executed to keep me interested. Clichés are boring. I read
zero webcomics that are about guys playing videogames. And I
like games.
I tend not to read many "serious" story-driven comics where there is little to no humor, no punchlines etc, mainly because the ones that have decent artwork update so slowly that it makes it difficult for me to get into the story - I'd prefer to read such stories in a printed version when it's all finished, much like a regular novel.
My regular webcomic reading list used to consist of over 30 webcomics, now it's less than 10 - partly because some of my favourite comics ended, or went on infinite hiatus, but also because some comics just weren't worth my time any more.