isn't that a bit of an exaggeration, especially if you have experience with other functional languages? maybe if you've only ever written JavaScript prior to trying Elm…
I programmed in functional languages prior to writing Elm, but the reactive part was new to me. I found the signals primitive to be pretty mind-blowing. I haven't programmed in Elm since then, and some time ago they simplified that feature into other language primitives, so I'm not sure what it's like now.