Babbel is structured a bit like Rosetta Stone, in that it is heavy on pictures, and in that it offers a voice recognition feature. It differs from RS in that it relies upon word/phrase equivalency with "native" language (I used English, I believe you can set your native language but I haven't tried it). There is a nice little chunk you can try before you buy. The pictures are clear. They used what sound like native speakers. The words I worked through were at least as plausible as RS's. The dictation/spelling portion is more incremental than RS, in that one part of it just asks you to pick the correct first letter and another section offers you tiles to spell the word/phrase with. Those are both valid pedagogical strategies to (demonstrate that you are) learn(ing) how to read/write/spell a language.
The voice recognition feature suffers from approximately the same set of issues as RS, altho they handle the first syllable/communicate when you can start speaking marginally better.
Babbel is potentially highly disruptive of the RS revenue stream altho it suffers from offering fewer languages/only lower level courses in many of those languages.
If I had not already bought RS, and was looking for an online method for learning/reviewing Dutch or another language, I would start with Babbel. Because you get unlimited access for a period of time, if you work for many hours diligently, you could save a ton of money over RS.
If I decide to learn another language after this summer, I will be looking even more carefully at where Babbel is at that point.