The contents looks interesting and useful and the theme is fine.The header is too dark and not well suited for the entire theme.
well, i think that is a template modified. I don`t say it is wrong, but because you modified it it gives the whole design a unique look. I would suggest considering an image header, gives a more professional look. The main piece of the site is the header. That is what comes first to your eyes. The top part of the site. That is why you want it to be as attractive as it can be. Try using something abstract, combine the colors of your site in the header and you`ll get a really great unique look. Hope this helps.