Not helpful anymore - this is over-the-top frustrating!
I have used Duolingo a while ago for Spanish and liked it and also when I started studying Czech. Now, after everything has been renewed, I am trying to get through the exercises. After just a few topics that I covered up to level 3, I am now still as a beginner on level one of some new topics, e.g. family. But there is actually no way to understand or know the solutions with basic Czech. The principle of studying words or simple sentences on level 1-3, which used to be so helpful, before moving on to more complex sentence structures has been completely removed. Now I am entering level 1 of a topic and have to deal with 3 different cases and all their declensions of articles verbs and nouns, possessive articles, object pronouns and prepositions at the same time along with new vocabulary. By now I am at the point, where every single sentences basically pisses me off and I have lost all motivation to go on studying with Duolingo. I am utterly disappointed that Duolingo has turned this formerly helpful website into such a mess. I don't know if that is true for other languages but it is definitely not a website anymore that helps beginners of Czech to study the language. I will go and look for another course, and I don't mind paying for one either, so it is not that I think Duolingo should offer everything for free (I am not ungrateful that is), but I think if this is what they are offering for free then it is definitely nothing I would be willing to pay for.
Czech is much more grammatically complicated than Spanish, and there is no magic way to avoid having to learn a multitude of different case endings. Perhaps they could be introduced more slowly, but there really are a lot of them, and 'simple sentences' in Czech require that one knows certain cases that would not be necessary for correspondingly-simple sentences in Spanish.
I think it could probably be improved, particularly at the beginning, but the language itself is a limiting factor, and moving more slowly would probably result many more much less useful or interesting sentences, which would undoubtedly lead to complaints from other people about those. I do, however, appreciate the evident care the Czech team has put into the design of the tree; it really could be very much worse (try the Hungarian course).
I studied Spanish but I do consider Spanish a fairly easy language (to me anyways as I studied French in school which has many similarities) and I wouldn't compare Spanish to Czech. I'm a German native speaker and teacher with a Croatian background (I cannot speak Croatian but because of my family Slavic languages don't sound "alien" to me. That means that pronunciation is not an issue and neither is the concept of cases including mutiple declensions. But I think there is no point in throwing all of them into a few sentences plus prepsositions plus possessives when they haven't been properly introduced. There is nothing wrong with translating a few phrases that are no actual sentences to get some practice and to get used to the patterns. I'm thinking "Frantisek's daughter", "Frantisek's son", same with father, mother, so you see the differences, instead of "Where is the big castle of Frantisek's little daughter". We're looking at a beginners' level here. I know that many people nowadays tend to despise drill as a language learning technique but it is actually helpful for beginners. I think the course as it is is probably useful for B1 students who want to work on some basic mistakes that they still make here and there.
I have only done the first two skills. I'm at crown level 5 and I still don't remember basic vocabulary. I'm not sure why it's so hard for my brain to hold on to simple adjectives like "other" vs. "different" vs. "wrong". If the later skills start off as challenging as you describe, I'm sunk.
Here is a great grammar resource for Czech; I've glanced at it but haven't spent time with it. One of the developers of the Czech course mentioned it once and I bookmarked it: