If not designed with accessibility in mind, Learning Management Systems (LMS) can pose accessibility problems for students and instructors with disabilities. Depending on the features enabled for a given course, students with disabilities could find that participating independently and effectively is nearly impossible. Some LMS tools—Discussions, Quizzes, Chat, or Wiki tools, for instance—can be more problematic than others. Learning Management Systems are becoming richer and more complex applications, and if they are not designed with accessibility in mind, it can be next to impossible to make them accessible and usable to users with various needs.
Important LMS features depends on your specific requirements. For example, a LMS solution that is successful for a University it does not mean that it will be successful for a large organization. This is why I listed the 99 LMS features in alphabetical order and not in an importance order.