It depends on what you want to accomplish.
If you're only out to please yourself or you have a group with original characters from a common medium (and RP, an online game, an avatar program) and you want to hang out with them ~ it doesn't really matter how dramatic, well-designed or well-made your costume is.
If you goal is to fit in ~ make a costume that will cater to a fashion trend within your fandom. Your goal is to blend ~ not pop... so as long as you don't go out of your way to do a phenomenally crappy job you should be fine
If your goal is to attract attention ~ you need to wear something eye-catching and outlandish. This can be both good or bad :P
If your goal is to attract only good attention ~ you need to create a character design that's both eye-catching and aesthetically pleasing/interesting to others. This is pretty tough to do since you need an eye for color, and a bit of talent for design/construction.
There isn't a standard for anything. People like what they like and hate what they hate. And most probably won't look at you twice either way
They'll be too busy engaging in their own fandoms.