I really like the new system with word stregth decaying; it really helps me remember those words I would otherwise forget. But there seems to be a huge problem. I can go through a lesson, and get the same word wrong the first two times, right the third time after peeking, and still get perfect word strength. This makes no sense; obviously if this happens, the word strengh should be more like "weak". And then the strength doesn't even go down for weeks. And even if I get a word right 2 times in a lesson, it often means that I just happened to be able to remember it for a couple minutes, and I completely forget that word once the lesson is over. I understand that there is a "practice weakest words" button, but it doesn't seem to actually give me my weakest words. Overall, I pretty much just think that the algorithm for determining word strength needs a lot of work. I definintely wouldn't mind having to review more if it meant that I am learning the language better.
Although it shows full freshness immediately after the lesson, words that you've consistently gotten wrong will decay faster than those you have not. We're improving our models based on the collective experiences of all of our users and plan to make the model even more individualized in the future!
I like the idea of pointing out the strength of the words! I just think that the "Practise weakest words" doesn't work very well, because from my vocabulary list I can see that I have words with 3 out of 4 squares of strength, but I still do not see these words in the exercises. Instead the exercises give me words that are with better strength than my weakest words.