In Hebrew the adjective always goes after the noun. However, in English: You are good women and You, women, are good is NOT the same thing. SO I would say: אתן נשים טובות, לא רעות - you are good women, not bad. However, when I speak to friends informally. I can say: you girls (rather than women) are good! This would have been in Hebrew:נשׂים (בנות). אתן בסדר or even better, you girls are 100% (an idiom for saying somebody is very good): נשׂים (בנות). אתן מאה אחוז The problem is that you cannot translate things literally from one language to another. So in Israel, you would have said: you girls are 100%.
But in another sentence/ exercise (I don't know how to call it), the translation for רעה is "evil", so when I translated by "mean", it was counted wrong. The strangest part is that it accepted this translation ("mean") for another sentence... So, yes, sure, translation is all about context, but with sentences like those suggested, the "context" is very limited
I'm not native, but I've definitely heard "lo ra" used to mean "not bad" before, as in "this movie isn't bad" הסרט הזה לא רע.
What I've heard more often is "lo nora" לא נורא -- not terrible.
באמת הסרט הזה לא היה נורא-be'emET haSERet haZEH lo haYAH norAH Actually that movie wasn't terrible (it's pretty good!)
Maybe a native speaker could help us out here :)
Confirming Theresa: לא רע is very common to express a positive opinion. Depending on tone and context it can vary from slightly positive to very positive (and so is prone to cause misunderstanding and offenses, say between close couples...).
Now, לא נורא is also very common, but won't work as in your example: it expresses a negative opinion, only not as negative as one might have expected.