These sites are only the tip of the iceberg when it comes to online courses. You'll find the most variety in course offerings in business and, no surprise here, computer-related subjects and programming. A good course will force you to get involved with mandatory discussions and chat room sessions. It makes it easier for students to ask professors questions and instructors have more time to type and plan out thoughtful answers. Arguments on online message boards can run wild at times, leading into back roads and tangents, but this can be a plus, as outspoken students aren't as easily silenced by a moderator.
Professors tend to stay in the background sometimes, to facilitate peer learning.
Some courses are great at interaction and discussion while others have instructors that barely make any contact at all except for the final grades. But you can't really tell that from a course catalog. The good classes will have students acting as active participants in discussion and learning from one another. You should be ready to have discussions and arguments with people from all walks of life, so don't be afraid to share your perspective and experiences. Read the Tips for Success for some good advice.