I am no expert in the design standards on here but as my job is testing a companies website, I can give my opinion on what I would class as issues.
The logo in the middle cuts into the navigation and although that may be by design, when you hover over the menu links below it (GAMES CONSOLES, STUDIO EQUIPMENT, ELECTRONICS), or when they are active, it just does not look very good.
The right and side of the header bar is just messy. The cart looks out of place where it is and also, the caret next to it made me think that it was going to be a dropdown [UPDATE: I found out that once you do have something in your cart, this DOES become a dropdown. I would recommend only showing the caret when in that state. Unfortunately, once you get to two products in the cart, the text becomes too long and the caret drops to below the text]. The space under Contact Us, Sign In etc makes it look unfinished.
With the navigation, on all pages other than the index, the white text on the grey background is hard to see,
Typography is very hard to ready in places, especially menu dropdowns and the footer.
The footer also has a lot of dead space to the right.
The style of the RTV i AGD menu dropdown does not look to bad, although I think it needs a better name. The rest of the menu dropdowns, however,do not seem to follow any style pattern and appear all over the place.
A lot of the product pages are empty other than a picture or a logo (eg. http://grafike.pl/1_electro_and_hightech/en/21-mobile-phones). The picture on the memory card page is also clearly being displayed at an enlarged resolution. Some of the pages are also completely empty (http://grafike.pl/1_electro_and_hightech/en/75-audio). All of this just makes it look unfinished.
On a product page that has the full details, when you scroll, the product image remains in place and you can no longr see the image or zoom buttons (http://grafike.pl/1_electro_and_hightech/en/television/1-faded-short-sleeve-tshirts.html).
Some other pages all look unfinished (http://grafike.pl/1_electro_and_hightech/en/content/3-terms-and-conditions-of-use).
The pop-up when you click Add to Cart also looks unfinished. The success message is too close to the top and the two buttons at the bottom are just awful. Sorry but individually they do not look good and as a pair they do not compliment each other.
The contact page looks very bland and has a lot of white space. The form itself could be better arranged.
Layout on the sitemap seems messed up. You have several rows but some only have one content area in them.
Lastly but not leastly. The animations. There are too many and they do not work well in most cases. After the second page load I was already fed-up with watching everything at the top slide into place, pause and suddenly jerk back.
As I said, I do not know what Envato’s reasons for rejecting were but those are most of the bits I would find issue with, without looking at what it is like in mobile view…