Around October last year I started learning: upper-intermediate-english course on memrise. It took me a really long time to finish it despite fast progress at first. Course is really long (962 items) and during learning you need to refresh words you have learned. It was really challenging to learn from half of course to the end. There was always something easier to do but finally I have finished it. Of course I still need to refresh those words, especially those I have learned recently but I really feel proud of myself.
As of course itself it's obviously long. Good thing that most of words have attached pronunciation and a couple of times I was really surprised so it is useful. Sometimes explanations aren't clear enough so I know without remembering it exactly which from similar words suits which explanation.
So I started to think what next. I have practiced bunch of words but they are just words, it's not that I'm using them. Some time ago I have added to my backlog list on Trello new course from Duolingo. It is still in beta but it's already really good :)
It's the English course for Polish speakers, if you are interested check it out: https://www.duolingo.com/course/en/pl
Good thing about duolingo is that I can see, hear and create complete sentences. If feels it would be much more useful in real situations that learning only words.
You can also see my progres: https://www.duolingo.com/krzychukula