I would prefer it if there was more explicit teaching of grammar on Duolingo (there are lessons on eg verb endings but these are few and far between) but I have a couple of bookmarked websites and a grammar handbook that I can refer to.
I understand the Duolingo rationale of learning more by osmosis, in the way that you pick up a first language.
I'm finding that I can write a sentence, look at it and often just know that I have the word order wrong. I'm starting to get a feel for how the language is constructed.
I like the way that there's a kind of spiral curriculum, with previous content revisited and integrated into new learning. That seems to go with what we know about short term memory and embedding knowledge into the long term memory.
I think that if you want specific vocabulary eg being able to order a meal and check into a hotel because you're going to use the language on holiday, then Duolingo is going to be frustrating.
But I'm using it as a stepping stone to eventually (I hope) becoming reasonably fluent.
At the moment, I'm still a real beginner but the apparent random vocab has been surprisingly useful.
Today somebody told me that this part of the country used to be much quieter but there were more people here now and more houses being built but still liked it better than the city that she used to live in. I could get the gist of what she was saying.
I could understand when someone told me that her eye hurt and she was seeing stars.
I like being able to have little random conversations. They're still ridiculously stilted but luckily people are patient and forgiving
I'm on my phone so can't scroll back but someone said about needing a hare mode on Duolingo to complement the tortoise mode.
Have you listened to the podcasts? They are on a particular theme and have a mixture of English narration and native speakers talking at what seems to be a fairly natural speed.