1. Leverage Mobile: See HN in your mobile, can you read it to me please?
2. Padding: Look at the numbers to the left (numbers inside <td> tags, are you using a for loop? hehe), can you see they are 0 pixels from the side of the page, why? Are those numbers needed anyway? I find it difficult to read and click the article I want to read, the posts are too close!
3. With more padding and a bigger font everything should get much better to read and process, not just for mobile...
4. The colors seem old-fashion and not in a good way if you ask me but if that's the branding that's fine, just do it right. For instance, look at the top-menu, open up your browser's inspector and change the color to white, much better ah? The "active" can be something else.
5. I would underline the article links on hover, it makes it easy to see what you are clicking.
6. The gamification controls are weird. Example: 126 points by user 1 hour ago | 26 comments ... See how it looks like "user" gave 126 points to the article? What about: by user 1 hour ago | 126 points | 26 comments ?
7. Separation: Maybe enclose the articles in boxes of some kind or just throw a line between the articles, it is so close and compact...
8. Submission form: why not adding some optional WYSYWYG goodies? If the limit is 2000 characters why i have to hit submit to find that out?
9. Ah, TABLE seriously?
These are just some of my findings (2000 chars limit). I would recommend other kinds of ordering, ability to curate the listings somehow, etc, but for now let's focus in the UI/UX. I'm hereby offering my services as developer to make this happen, let me know!