Busuu

One thing that sets Busuu apart is some of the exercises are open ended questions, which are then rated by other members who are fluent in the language you are learning. I think it's really good to have moments where you aren't just doing multiple-choice, fill in the blank style quizzes, but are actually trying to express yourself.

I studied French in France, and it's in those difficult times when you are really trying to communicate that you can learn the most. The less algorithmic the approach the better, imo.