Not OP and not a professional Crystal dev (not even a Ruby hobbyist). But I use other languages professionally, including Java, Python and (to a smaller degree) Rust.

But my $0.02: what Crystal does best for me is the "fun factor". It has a very good balance between a dynamic language "feel" with the safety of static typing, and with native compilation.

I can just prototype things willy-nilly with minimal ceremony and not worry too much if it starts getting big.