My biggest thing is when I get interested in a character and find that they have mini series or runs that were intended for an ongoing series where
1. the writing is terrible
2. the art is awful
3. both of the above together
4. the writing is passable but the art is garbage
The most recent experience I had with this is the newest She Hulk series its so boring, hamfisted, the artwork is flat and uninteresting.
Here's a few more things that piss me off about comics
Agenda pushing, just write a fun story no one cares about where the writer stands politically, besides how memorable are they really we tend to remember the more ridiculous fun adventure types of stories way more often than not.
When a writer doesn't care about the characters they're writing for or just doesn't understand them.
Pastel color palettes used on generic pencils
When a company changes things because a group of people who don't buy and will never buy a book they make whines about things being offensive and ruins it for the people who actually spend money on the books.
When writers have characters make ironic comments about their own books in a main series, characters who fall more in line with Deadpool and Harley Quinn don't count.
Obvious topical themes, kind of falls in with why I hate agenda pushing, more often than not I just forget about them and its mostly just lazy writing.
Also when a book has to line up with things that'll be seen in a movie.