Warning in advance: I saw this topic and got a little to excited to respond. I do not mean to offend.
The number one thing I am tired of in comics (and specifically, webcomics), is the lack of an Editor. I don't mean spelling/grammar (though that is frustrating), but mostly the recurrence of this story format:
Beginning, Middle, Middle, Middle, Middle, Middle, Middle, Middle, Middle, Middle
The only thing worse is this:
Beginning, Middle, Middle, Middle, Middle, Middle, Middle, Middle, Middle, Abruptly Cancelled
We don't know when to quit! This doesn't necessarily apply to slice-of-life/gag-a-day comics, but is especially true in manga and American ongoing dramas (whether fantasy, sci-fi, superhero, historical, etc).
Everybody wants to make these giant, epic tales, but rarely do we complete them, so we are left with many stories without end - adventurers who constantly do more things, but do not grow, change, or learn lessons. We also tend to spend time exploring the world and the various things in it that we can lose track of the plot and forget why the audience was invested in the first place. It is fine for some stories to be sweeping, meandering sagas of Character X in Unique World Y, but when it is every long-form webcomic, it tires me. I would love to see more webcomics like Battlepug, Ratfist, Penultimate Quest, and Delilah Dirk & the Turkish Lieutenant - they started, they had adventures, and they ended (or are about to end, like Battlepug). I miss them when I'm gone, but I can always re-read... besides, it's fun to see what the writer/artist can do next! The writer can even do a sequel, but it's not just Chapter 1 and Chapter 2, it's separate self-contained stories!
If you are offended by what I say, your comic may be the exception to the rule, but if your ending is still 3000+ pages away, just consider if all of that space really helps the story or simply extends it. Remember the lesson of George:
End on a high note, and get out!