I've seen some great cosplay's, but I've also seen lots of awful ones! I think if you somewhat look like the character your portraying, then go for it otherwize it looks silly.. Well most of the time it looks silly anyway really, lol.
I apologize if these have already been posted!
These are some of my favourites:
This is just so cute!
This is probably the worst one I've seen, I was like omg when I first saw it! It' so revealing, ugh.. How does she go out like that??
Furthermore, I do not believe in 'bad cosplay'. Though I never cosplayed myself, I don't think it's wrong for people to try, it's supposed to be just for the fun of it ,right? So even that *wonderwoman* cosplay is awesome because you can tell she spent ages making her costume!