I like:

- community, of course;

- minimal design.

I dislike:

- only total score for comments (no up-votes vs down-votes);

- no folding;

- no tagging;

- no way to "watch" discussions or comments;

- "More" link at the bottom of each page expires (thus you have to start from front-page again, not nice if you read HN not that often);

- no way to join discussions whenever someone find duplicates;

- no contributions section (searchyc.com (which seems abandonware, btw), pages with best discussions by topic, etc.).

EDIT: I dislike HN not being able to format an item list.