Notable differences from a user-visible perspective:

• Upvotes and downvotes are tracked and displayed separately. This makes a clear distinction between a controversial answer (+20/-20) and an answer that nobody has voted on (+0/-0). On StackExchange these would be indistinguishable without the privilege of being able to view up and down votes.
• Comments are threaded, and threads are collapsed by default. This helps to reduce the level of comment noise that is typically seen on high-visibility StackExchange questions, and encourages the use of comments for their intended purpose: to suggest improvements to answers or request clarification of a question (rather than to soapbox, or offer low-quality semi-answers, as is often the case on StackExchange).
• Both up and downvoting is available to all users without being gated by reputation. I'm not in a position to state whether this is better or worse than requiring a minimum rep to downvote, but it is the currently-implemented policy.
• "Accepted answers" do not exist. Instead, you can apply a badge to a particular answer, which states "Worked for <person>", but this does not bless the answer with a prominent green tick or pin it to the top of the list of answers. This allows a questioner or any other user to thank a particular answerer for solving their problem, without subverting the ranking system or promoting a possibly low-quality answer that happens to tell the questioner what they wanted to hear.
• The Code of Conduct is reasonable, straightforward, and based on common sense rules that encourage a civil and constructive learning environment, rather than a tool for pushing a Silicon Valley ideological agenda. Long may it remain that way.