I really like the format and premise.
It doesn't seem, however, to be sufficiently flexible in the various ways to fill in the blank (at least in Russian). For example, when given the sentence
Как вы на это ___
with the translation "how did you see that", I tried "увидел", and it told me the correct answer was "смотрите". That's clearly another answer, but I'm not sure it's any more than what I gave. Or perhaps my Russian isn't as good as I thought?