In short: lots of theory.

Longer version: Computer Science at Harvard is full of a lot of people who are excited to put a lot of time into their studies, and who expect to get a lot out. For the most part though, the required courses teach you a lot of theory and the electives can give you real coding experience if you want them to. There is a lot of cooperation that happens during psets and overall the environment is very collaborative. Many students who study CS go back and serve as course assistants for courses they have taken, and people are generally pretty willing to sit down and help you walk through anything if you ask.