I think it's generally a good thing. Shows you're interrested in something, devoted to it, and isn't afraid to have fun.
I only have two gripes with it. One; cosplay your gender, please. Sorry, but if you're a 6.2 male, then cosplaying a chick from a japanese anime won't work. Likewise a 4.5 small girl won't manage to cosplay a t800 terminator. And two; dressing like the whore-version of whatever you're cosplaying, to get attention.
With that out of the way, i want to repeat that i think it's cool. Some cosplays are amazing!
It can be pretty cool. I've never done a good one, but I hope to at some point, if I have the money to actually make the costume :P Ideally, it'd be a group Hellsing one and I definitely want to cosplay Seras:
It's a wondrous celebration of fandom and popular media. I enjoy it, though I don't practice it myself. However, I feel the cosplay that most people see is the over-sexualized, professional model level cosplay that is generally used to draw in viewers or clicks on a website. It's so much more. Sure, sexy cosplay is fun, but I've seen come costumes that took a lot of ingenuity and creativity just to get it to work in real life. It's amazing.
Cosplay, in my eyes, is just a bit of fun. Yeah, it can bring the inner creativity out of you if you make your own outfits. I used to cosplay regularly when I was a little younger but I rarely have the time to play dress up nowadays.
I can't speak for the boys, but, on the girl side there seems to be this... coldness, toward women who are more traditionally good-looking, at a lot of the cons. It seems almost like a girl edition of the movie "Revenge of the Nerds".
Dunno what's going on there, but, it almost seems like there's a "safe space" for women who were rejected by the popular crowd growing up, and that space is protected pretty (passive-) aggressively.