Am new to duolingo and started my first learning with Spanish..so far am thoroughly enjoying my lessons which explains how in 4 days am 6 levels up! I love the ways these guys have designed the course and its indeed an effective scientific way to push new knowledge deep into the already crowded brain. Hope to see myself speaking Spanish soon!
It is an amazing course, I did get to a section where I got bored though so I added another language which motivated me to go back to Spanish. I also used some other sites and read magazines in Spanish it was V.Past - V.Fut Phr (still on it) that I am finding so draining and boring. Just remember what you want which will keep you motivated to keep going.
Also I found doing English for Spanish speakers to help.