One pain point of my using Crystal! The crystal play borne playground is painful! When I copy the code from the book and paste it there, clicking on Run Formatter does nothing. The error labels often do not go away, and it crashed on my multiple times. Not sure it should be supplied with a Version 1.0 system.
Maybe Elixir spoiled me, but having a good interactive system (along with good IDE integration) receive strong points from me and Crystal receives low points in them both.