Double outline bubbles. They don’t look good imo
Isekai being butchered as a genre, falling to villainesses who are not villainous and leveling up dudes.
I think my biggest issue with the genre has to be people... not taking advantage of the concept that you can turn into ANYTHING. Things usually revert back to RPG mechanics which does suck, but I can see why that type of stuff is popular in Japan since they're obsessed with RPG's.
When I made my comic I was kinda shocked no one did the stick figure idea.
the webtoons style mismatch of heavily 3D backgrounds underneath relatively flat character drawings.
The main character is the chosen one. It's boring.
This. I understand not liking to draw backgrounds but this is just lazy/annoying. Specially when it doesn't match at all.
I heard this is done because they put the artists on such a tight schedule that artists have to try to find things to help cut back on drawing time. I sort of wish they were better at putting filters on it so it doesn't stick out as much.
Stories where the objective isn't to break down the oppressive regime, but to be the next one. I was baffled the first time I saw it and I still am every time someone makes that a thing in this day and age.
Not "we can rule better", straight up "I want what the abusive ultrarich CEO has".
For me personally there is too much action and violence in comics.
I maybe found that entertaining when I was younger, I´m tired of it now
Fantasy intro schpiels.
"In the year 1364 of the Caldean calendar, Duke Nerideth of the kingdom of Ansalor convinced King Ansalis XIV to invade the neighboring nation of Luriden..." blah blah blah
I've read so many of these 'prologue chapters' that seem to think the most enticing way to introduce their story and make me excited to read it is by giving me an excerpt from a history textbook.
Several of them are actually good fantasy stories, but they are actively made worse by these mindless narrations of names, places, gods, religions, and magic powers that all get explained anyways over the course of the story. I actually just skip these whenever I see them now: If the story NEEDS that intro schpiel for me to understand what's going on, it isn't doing a good job of worldbuilding, and if it doesn't, then I'll learn everything I need to know when the information becomes relevant anyways, so why was it even there?
Related to above post: intro narration as an excuse for lazy art.
I just hate when I open up a comic, and the art, instead of being well-drawn pictures of things, is a bunch of scribbly scrawlings, vague silhouettes, stock photos and often with crappy photoshop filters over the top, just any excuse to avoid drawing an actual place, object or person clearly.
Load up the comic... bunch of black space... Then some scrawled stick people I guess are meant to look like cave painting or something, but they just look like half-arsed stick people because no effort or research was put in "Long ago, the people of the world lived in harmony..." Picture of some stock fire "But then... there was a war." picture of a stock bloodstain "Many people died." Generic star texture "But now a new legend will begin?" cliched manga stock image of drop creating ripple in water.... and then I return to the forums where the artist is like "Why is nobody reading my comic, I put so much work into it!" ....Did you though? DID YOU? 
Like okay, if you want to make a comic with lazy art, and avoid drawing things that are hard or take time, then go for it, that's fine, but don't do it and then expect people to treat your lazy comic like it's on the same level as ones by people who understand that if you want to entertain an audience, you need to genuinely try to show them something well-presented with art that tells the story, not just words floating in space and occasional vague imagery chosen based on how easy it was to put in, not how well it tells the story.
Idk I feel like this sort of thing is done by developing artists who want to tell stories, overestimate their own skill, expect praise for something that they worked hard on, but isn't very good.
I don't think we should shame people for not being technically skilled, if an unskilled artist wants to tell a story that they don't have the ability for yet they should, we have all been there making that epic saga in the backs of our notebooks with awful designs and bad backgrounds where we're scrambling to hide the hands. And if someone takes that and posts it on the internet, that's fine.
Of course you do reviews for these people sometimes which I can understand to be a more frustrating process - I would wish no-one the misfortune of reading my first scifi notebook scrawlings nowadays.
I don't think you really get it 
also it's not necessarily an amateur creator problem, you will probably find a good dozen or two of this kind of comics being Originals here on Tapas. It's just a lazy way to introduce the story, that's all. You will find it more frequently made by beginner creators, but not exclusively.
Jumping on the 'fantasy intro schpiel' train - at this point complaining about them is as much of a trope as making the in the first place, but there are specific things they always include that I'm tired of seeing XD Like it's always seems to be some combination of:
- creation
- gods
- wars
- factions
- people dying
- new legends beginning
Like goddammit, give me some fantasy intro schpiels where something interesting happens 
Even just zoning in deep on one of the above points and telling us why the war was interesting and why we should care about it over the other 8354 generic fantasy backstory wars (e.g. Woven6 on Webtoon) is good in my book. That's how you use your prologue to actually hook people
Hm, I get what you're saying, though I also get the impression Darth Mongoose was more ratting on using stock images/filters/etc as a crutch/to hide one's weaknesses moreso than the skill level of the artist. I feel like she'd respect someone who makes an attempt to draw something non-generic with their own hands, even if it's a crappy attempt because they're an amateur. Then again, I get that amateurs feel more pressure to hide their weaknesses. Either way, I agree on not shaming amateurs for being unskilled; I just don't feel like that was the intention here 
Yeah, as Lemma and Kelheor said, I'm not really against people who can't draw so well yet, or even really people who bite off more than they can chew and replace some panels where they planned to draw something difficult with something easier like silhouettes, or a simpler image that hints at something. Because I think a lot of us did that on our early comics; going in like "Aw yeah, I'm gonna draw a comic- oh no, oh crap this is hard! Oh geez, is it always this much work? why is this taking so long? How do people make multiple pages of this a week!?"
And the important thing is how the artist reacts to the discovery that comics are hard and a lot of work. They could treat it as a learning experience, "Okay, this comic is kind of crappy... but I'll learn what I can making it and my next one will be better" and then learn to either work smarter (finding shortcuts that still look good and clearly tell the story), OR work harder (just knuckle down with a new appreciation for how actually most good comic art is literally just somebody applying either a lot of effort or a ton of experience). Or they could treat it like a cosmic injustice, where their struggle with drawing is somehow different and more special than everyone else's and it's not fair, so people should read their comic and not give feedback like "do more visual storytelling if you want to make good visual storytelling-based media".
I would seriously much rather read a badly drawn comic making an actual effort to tell a story visually and draw things the artist finds hard than one where there are sparse very well-drawn panels, but as soon as the artist gets a hair outside of their comfort zone (which is often just a person facing forward standing still looking pretty) or might need to draw something detailed (like...more than two people in one panel! OH NO! Or...a person walking through a room with things in it! Oh, the humanity!!!) the comic is suddenly showing me a disconnected montage of random textures, gradients, close-ups of random objects and silhouettes that make no sense.
I have a few, although I speak more as a general writer than as a comic enjoyer:
First, the prologue that serves only to give a deluge of information to the reader. This is a very common gripe as is evident from this thread, but my issues with it aren't solely because it's "lazy". I think anything if done in an interesting way can be good. My issue with such introductions however is that often times its purpose seems redundant, as you'll likely have to re-introduce/explain certain bits of lore later down the line as people may not remember, and at that point it makes you wonder why you needed that prologue in the first place. Information should be given when relevant, and it should for the most part be given as naturally as possible.
Second, and this is more of a general story-telling thing, but the lack of notable flaws in characters. At best you get things like being clumsy, clueless, or being physically weak, but to me that's not much to get interested in. I enjoy emotional conflict as much as I do physical conflict, so it's admittedly disappointing to see very little of anything of the former that goes beyond surface-level issues. I like to see genuine, crippling flaws in a character's personality that makes them cause problems, make enemies, and is something that they try to actively work towards fixing. your character doesn't have to be a jerk or an anti-hero for this of course, you can have a more "heroic" protagonist or side-character and still give them some kind of imperfection in their soul.
Lastly, there is something I prefer to call "Lore-Bloat". this is more common in newer creators but it's when a creator has so many ideas that they wish to utilize while having a comic that can only carry so much, but they decide to cram everything in rather than just save some of that creativity for a future project. lore is amazing and can bring great depth to your story world but there comes a point where it becomes too much. bloat can cause the story to become convoluted and confusing, making it hard to keep up with the work, or alternatively there's a great portion of content that has little to no connection to current events so it feels more like useless trivia.
I’ve never seen this before but through a person who makes comics this is strange.