I feel like I'm not being required enough to produce (I'm specifically studying spanish now), and when I finally am I have a lot of trouble. Also, I might get a word wrong over and over, and then be given several words I know well and complete the lesson... even though I still don't know the word, and never end up learning it. Is there a way to force me to repeat words and not give me words repeatedly if I keep getting them correctly?
You will eventually. They are trying to reinforce things slowly over time, including words you will know better than others so you don't go on to forget those, since you really can. When I first started various languages, I thought I'd never forget the words for things like 'water' since it comes up all the time on here at the start, but the other day, I found myself not quite able to recall the Danish word for water (vand). It looks like you have only been doing Duolingo for a short while. Sincerely, it does work. You may not learn a word on a particular day, but it will keep coming back if you keep your trees gold, and eventually, you will know it.
In my experience, Duolingo works best when it's one brick in the wall. It's good for exposure to concepts and the language--and it's not necessarily a challenge.
If you really want to drill vocabulary, there are Duolingo-specific flashcard sets on Memrise and Quizlet. If you want to learn more vocab (but not in a drilling sort of way), Babadum is pretty nifty.
SpanishSpanish.com has games and "games" that practice vocabulary and certain concepts. StudySpanish.com has concept-specific practice. MosaLengua and MindSnacks are also apps that help practice phrases and dialogue, if that's of interest.
In other words, telmacblack, if Duolingo isn't enough of a challenge for you right now, stretch yourself! There is a lot out there. I've basically been maintaining my streak (by doing the Spanish-to-English tree) and am getting the bulk of my language practice elsewhere.
So much agreement! I mainly just use Duolingo, but that is because I use it for languages I am learning for fun or to maintain ones I have already studied in various other ways, so I am learning the Germanic ones just because I enjoy it and it's good mental exercise and I keep up with Spanish and Portuguese with translation. If I suddenly, say, had to move to Oslo, I would be doing so much more than just this to learn Norwegian. If you are serious about learning a language, this is just a good foundation, a springboard to help you do other things. Spanish in particular has so many resources online that are both free and good, same with German. I would say Duolingo is a good way to get started with a language. If you do the whole tree and get up to level 25, you will probably have an intermediate command of the language, but obviously that takes time. If you want to speed it up, add other things in.
This isn't really a solution - I have other materials, but the problems with duolingo are ones that are really easily solved (like a single option to disable the choose-from-a-list ones and replace them with writing out spanish translations of english), which is why I mentioned it.
Sure, but those aren't in the users' power right now, nor does it seem like Duo is interested in following industry best practices for test making (e.g.). Duo doesn't sound like it's ever going to be the finely-tuned, customizable service that is out there. I've dealt by reframing my expectations and looking elsewhere. It sounds like you have too.
Rotating your phone usually turns the "construct a sentence from these options" questions into written ones, if that helps.