I tried to put these in some kind of order, but I like so many features so much, I fear I failed.

• Content. Content. Content.
• The on-topicness
• The Monks
• The expertise
• Near enough ad-free
• I like that so much of the site is customisable using CSS
• XP & voting
• Nodelets
• The ability to add your own links & especially the Add current node link to your Personal Nodelet
• The /msg system
• The XML tickers
• The CB (despite the fact that I never use it) - I do read what you lot are are talking about :-)