I think everyone is going to have styles they don't favour. I don't typically favour hyperrealistic styles of art. I like styles that are more flowing, abstract and full of personality. And even though many could see manga-style as generic (and those that try to replicate it), I enjoy it's simplicity. I don't really like the mindset that if you can't replicate a style perfectly, that you shouldn't be doing it. It's art, and everyone's free to have their own interpretation of everything. People are going to build their own style off of something, as it's hard to have a style that's truly original these days (not to mention that everyone has got to start somewhere. We can't hold off forever on posting our art, being afraid if it's not absolutely perfect before getting it out there).
In terms of art effects though, I'm not that big of a fan of people that quickly use the airbrush, with thin, sloppy linework, as the TC said. Some people can use the airbrush really well, but if you're going to to combine it with sketchy linework like that, it's just not a pleasant combination to the eyes. Either keep the lines cleaner by providing a sleeker inking layer over the image while getting rid of those sketchy lines, or stick to black and white (or even flat colours with your sketchy art lines). Also, I've really come to appreciate backgrounds since I've posted on tapastic. Not every panel of a comic needs a background, but I've seen some that flat-out ignore them. With the exception of some comedies (or sometimes slice of life, which I don't really read), I think those added details are very important to draw readers into the atmosphere of story-based scenes.