Duolingo barely scratches the surface, and at the same time, in many ways, hinders progress for beginners (I've seen people struggle with things they shouldn't have to struggle with). I wouldn't recommend it to anyone.
Could you give some examples? I've never used Duolingo for very long, but I had the impression that they were making things too easy, especially with multiple-choice/sort-the-words questions where you can often guess the correct answer.
Translations make me spend time worrying about how EXACTLY the original translator phrased it rather than focusing on the contents of the sentences.
I believe IBM actually implemented something like this as part of their "Watson" efforts, but there's certainly not a public solution around.
That doesn't mean it's impossible to offer useful translation exercises, though. It means it's impossible to use a computer to grade them. If you, as the student, are willing to ignore whether you get marked "right" or "wrong", you get the full value of the instruction -- you make the attempt, Duolingo tells you what the sentence meant, and even though Duolingo can't tell whether your sentence meant the same thing, you can.
I also use it slowly, read the words aloud, vocalizing everything being said.