Short answer: no. If you care for the long version:

It has it's strong points, but personally I think it has too many weaknesses. I worked through the entire Spanish tree shortly after I started teaching myself Spanish and I think it helped, but not much. Pronunciation - or at least exposure to proper, natural pronunciation - is extremely important and useful early on, but Duolingo has those ridiculous machine voices. On top of that, they present you with some pretty ridiculous and sometimes creepy sentences that no one would ever say.

I think the best thing Duolingo has going is the translation part of the site where you work with the community to translate uploaded material. But even then, there's much more to language learning than translating texts, so at the end of the day it's sorely lacking, even as just one resource among many.