The really important questions in any modern language:
(0) Does Crystal have a lot of undefined behavior like C?
(1) Does understanding Crystal programs require a lot of trial and error just like in Ruby?
(2) How good a job does Crystal do at preventing me from shooting myself in the foot?
A language isn't to be judged just by the amazing programs you can write in it. (Turing-completeness and I/O facilities have that covered.) Far more important are the totally stupid programs that you can't write in it.
(0) Does Crystal have a lot of undefined behavior like C?
(1) Does understanding Crystal programs require a lot of trial and error just like in Ruby?
(2) How good a job does Crystal do at preventing me from shooting myself in the foot?
A language isn't to be judged just by the amazing programs you can write in it. (Turing-completeness and I/O facilities have that covered.) Far more important are the totally stupid programs that you can't write in it.