The speed you get feedback is the key imo. When I use a language that has a repl I usually find myself using it more than the text editor / ide. And in my experience there's a nice side effect too: since you cannot write too much in the repl, you end up writing smaller functions that leads to more modular, reusable code.
For newcomers I'd suggest this introductory course by Erik Meijer: https://www.edx.org/course/introduction-functional-programmi... . It's about FP, not strictly Haskell, but it really helped me starting with it and really stimulated my curiosity (and he really can explain hard concepts in a simple way imo). I started reading the book after I completed the course and helped giving an answer to a lot of questions I had during the course.