I don’t have any experience with the course by @Paul_Wilson, but I see that it’s in alphabetical order. I once tried a Spanish course that was alphabetical and hated it…
I’m currently working my way through the one that’s sorted by frequency (by @ponchoosh), and enjoying it. It has at least two active contributors who have either completed the course or will soon. Very few words lack audio. I’m about 2600 words into it, and I’ve seen very few errors.
There is one small quirk, though. Earlier this year, a few words in the database were replaced, and they’re still connected to the mems and audio for the previous word. Once the contributors realized the problem, they changed the way they were editing the course, and now they’re replacing the audio for the new words. It’s a very minor problem, however, since it effects fewer than 1% of the words in the course.
I believe there’s worth in learning the top 2000-5000 words of the language you’re studying. Yes, you need to see those words in context, and you need grammar, practice speaking & listening, and experience reading & writing, but you also need vocabulary. If you don’t know the words, it’s very difficult to understand what you’re hearing or reading.
Memrise is the best tool I’ve found for learning vocabulary. The mems and SRS work really well. With a course sorted by frequency, you can work as far as you like, for as long as the vocab is relevant to you. If it gets boring 1/2 or 3/4 of the way through, than it’s time to drop it and focus on learning vocabulary that’s relevant to you.
As you’re working your way through the course, find ways to use those words in context. Read blog posts, listen to podcasts, read books for children and teens, watch movies and television, do a language exchange, take a lesson over Skype, and write.
Viel GlĂĽck!