To be frank, so what? Great book but I imagine a 'new costume' as you're calling it wasn't supposed to be a big deal here. Likely because she won't be wearing it all the time or ever again. The story itself is the centre piece here not the fashion. Of course she's wearing armour to go in battle for crying out loud.
I hate this aspect of comics media these days. Anytime Spider-Man or Iron Man has a new suit there's an announcement just to get people to fight on forums on whether they like it, which in turn gets everyone aware of the issue which will then sell more. Even this post is acting in that sense. This could have simply been Wonder Woman Preview.
On another note, I'd like to see Diana going between the previous design with pants and loads of others. It just makes sense that she wouldn't wear the same clothing all of the time, then people wouldn't be so falsely upset/delighted. She's a character not a costume.