very little passive tense
I am nearly at the end of the Greek tree and there has been very little passive tense. It hasn't been dealt with as a separate subject and only shows up now and a gain in a couple of sentences. I would seriously recommend introducing this skill as early as possible and setting sentences that use it it in when Greek is updated from the beta version.
It uses it enough. I've followed real Greek courses and I've lived in Greece. It might not be used as much as in some languages but it definitely shows up enough in both written and spoken Greek to be worth giving it a lot more attention.
Greek has updated from beta. We are now making a new tree and believe me, it is going to teach a lot of passive voice, as well as other grammatical issues that were not included in the first tree. About the passive voice, we are considering of having one skill for every tense. ;)