Each `lecture` is comprised of recommended reading material (sourced from LYAH, RWH, Typeclassopedia, and others) and some reasonably difficult homework problems that build on the learned concepts.
The Spring 2015[1] has a similar but different set of lectures/assignments. Do you think that is better/worse?
2013 starts with Functor and builds into Applicative then Monad. I like this a lot, as each builds on each other: fmap has a tight relationship with <$>, and Monad is pretty much Applicative with bind (>>=). Applicative is a Functor and Monad is an Applicative (as of 7.10 I think).
I'm by no means super experienced here, but the 2013 course was the first learning text that really got me into Haskell.
Yup, it's really tight: <$> is fmap
There were discussions on preferring Spring 2013 to 2015 here: https://github.com/bitemyapp/learnhaskell/pull/72 https://github.com/bitemyapp/learnhaskell/issues/40
The language and ecosystem are really mature now. But the main reason to go Haskell is simple and still the same: less bugs.