Make sure it's interactive. There should be a forum for questioning the instructor and chatting with other students, and there should be frequent quizzes and simulations. Avoid packages that are merely a book on a screen. Get follow-up materials. Be sure reference materials are included, and make sure there's a way for students to have their questions answered after the course is over.
Some vendors allow companies to integrate education packages into company intranets.
That makes it easier for employees to log on, and it's easier to present classes as a company perk. Only the most self-motivated employees will take courses on their own time, at their own initiative. Schedule a time during the workday for online education. Treat training as a meeting, and don't allow interruptions. Do not disturb.