Mine is art that is way too realistic and clean. I just can't see the emotions in to them. I'm not a fan of Marvel and DC either because of the same reason. I like to study them as references but not exactly something I admire.
Also, no offense to the fans out there but I personally I'm not that much of a fan of sakimi-chan's art. I just feel like her art looks the same even though she draws different characters and I just don't feel the emotion at all. Also other famous artists because the faces they draw look the same to my eyes.
Third, are those generic moe anime style. (ex: K-on, Chuunibyou, or any recent anime) I feel like every new artist are shooting for that style.
Art that are like the faces look identical and they only changed the hairstyle.
Senseless hentai/gore art that is obviously just a fan service and a cash cow.
Lastly, drawings that don't have proper foundation though I let this slide cus I know they're still learning.