Great concept. I've always been a fan of chess but never really played. I think that's going to change.
Feedback: You could use some work on your marketing message/brand. Chess has some much potential for interesting plays on the black/white concept and terminology. "More than just black and white.","Checkmate.". These are iconic chess ideas that I think if executed right, could add a the missing piece to the message you are trying to send.
I think the flat-ui is actually holding you back and with a few more iterations on your brand you could have a really unique presence. If you want to talk more, my email is in my profile. Hope this helps!