Basically it has to have unique content and rich content. Design plays no part in it. We are interested in offering sites with information not how that information is presented. There are some exceptions about affiliates and mirrors etc etc too. You can read the requirements in full here http://www.dmoz.org/guidelines/include.html
Come on Ivan, you know a completely unusable website is not listable because it doesn't give users the content that's expected from a listed site. How's the world domination thing going?
Don't be so sure, I've seen some fantastic websites with great content but their design made them totally unusable since after few minutes of trying you would give up and decided to return in few months hoping they would redesign it by then. I'm still waiting for you and bunny to tell me that my army made of millions of adorable huskies and bunnies with genetically enhanced supercutness which no one will be able resist is ready!
Wow. You're responding to a post written 1 & 1/2 years ago (Jan 2008) by a member whose last login was in winter of '08. Hope you brought along a book and a chair.