I think they're a fairly good way to get started and have some structure.
I feel that, perhaps biassedly, that the core way should be to build stuff and look up what you don't understand (not just bugs, also how/why things work). But maybe this should start at the intermediate level.
But there is a lot to learn in this field, and it can be daunting when getting started. I think MOOC can provide good guidance and structure, no worse than books, possibly better.
There are better and worse ones of course, but that goes for any information source.