It's quite a nice site and the tests are good fun but I go into a "test" and have to learn as I go. I'd quite like to see preparation videos that explain to me the subject at hand.
A good example is SpanishDict. I've tried it for awhile and I've picked up some good rules which help me learn new words and read words I've never seen before but still understand what it means and not just based on context.
Just an idea, reading and typing to learn gets boring and videos will help the visual learners a lot.