Which form of Latin is this? Classical, vulgar, liturgical, something else? I've only dabbled so far and it looks like Classical to me, but I'm not certain yet.
It's Classical, although there seems to be one quirk that I notice: I believe "ph" is supposed to be pronounced as a plosive consonant (a breathy "p" like in "pot") and not like the fricative "f." One of the voices pronounces "Stephanus" with "ph," while another pronounces it with "f."
I wonder why they put 'Philadelphia' in as a vocabulary item, if not to prove just that point.
The Latin is classical in pronunciation, and seems extremely well done apart from the aforementioned "ph" (which is honestly not that big of a deal, given that every Latin professor I ever had pronounced it this way). The Latin itself however is extremely artificial and simple, which has its fair share of problems, but also some advantages. I have around half of the course left to complete, but it would be next to impossible to read even a single paragraph of an Ovid or Cicero text through this course alone given its direction and approach. I do think that that it could be a great primer for those who are intimidated by the grammar to become acquainted with the concepts through interaction (similar to the Wheelock series' approach for self-learners), but unfortunately even when it comes to casually speaking Latin, let alone reading a classical text, having a formal study of the grammar is absolutely essential given how highly inflected the grammar is (it's about as complex as Sanskrit and Ancient Greek after all). Just see this as a gateway and a means of wetting one's feet with the language, and if you fall in love with it, then find a comprehensive grammar (A New Latin Primer via Oxford for example), acquire the motivation for drilling the declensions and verb inflections, and start reading Latin texts!
You're right. One needs to gradually learn how to tackle long and complex sentences and paragraphs in order to become a 'fluent' enough reader to read actual Latin literature. There is simply not room for such exercises in Duo as it is.
The other aspect which is leaving me very frustrated is the strictness by which translations are being 'graded'. As someone who studied Latin several years and regularly reads both Classical and Scholastic Latin, I am familiar with a whole slew of different styles of written Latin, and more often than not, the vocabulary and/or word order used here sounds very stilted and, as you say, artificial. And translations which seem the most natural to me apparently do not match what the computer has as the 'correct' answer. (The insistence, in particular, on a certain word order in the responses strikes me as the most artificial, and most frustrating, element.)
Is it really, I only listened to two pronunciations and first one seemed to no long vowels at all, the other seemed to lengthen completely random syllables. After that I did not bother playing more audios but perhaps I should give the TTS another chance...