Probably what rehashing what people have already been saying but the things I would like to see changed are:

Wider. Please please make it wider. It doesn't have to be a copy of old reddit but I find it distressing just how little space is used - 730px is just too damn narrow. It would be better (but not perfect in my eyes) if the sidebar was collapsible - I don't need to see it all the time.
Opening text and images inline is different - you click on the image to open it inline but the text placholder thing takes to to the post directly? I know you can press the little "book" icon but that moves between every post. I don't really understand this choice.
Related to the above - it sometime isn't obvious when a thumbnail is going to take you to another website or just open it inline. The little "picture" or "external link" logo in the top right sometimes doesn't show up at all well on dark images.
Can't say I'm a fan of drawing an orange outline over every single UI item I click on.
The main view should be more compact - honestly I don't really care for avatars but sure, I guess people do like them. If the view was wider the third line could easily be removed.
More indentation to the comments or an inset box -again less of an issue if the page was wider but I find the couple of pixels between indents not very visually distinct.

Don't get me wrong, the site is very usable and I'm not saying it has to be a direct copy of old reddit but I currently think it is very cluttered - so many icons and things going on in such a narrow space.