I think some of the comments here are unfair to Crystal and the careful thought (and lots of work!) that has been put into it. Projects like this should not be so easily dismissed as "also-rans".
I read through the Crystal language docs (meaning just the syntax etc) and as a seasoned C++ and Python developer who is _constantly_ looking for something with better performance (than Python) yet much cleaner (than C++), I think Crystal has a lot going for it so far.
Any "great" language should be able to take a thought in a developer's head and easily allow 1) the concise expression of that thought, and 2) efficient evaluation of that thought. I mean, those things we probably would all agree on.
It saddens me to say this, but C++ is falling over as a result of it's own weight. It's become a language for experts. Perhaps more than any popular language, it can take a simple idea in a developer's head and turn it into pages of code. It's actually quite embarrassing. I won't go into that further; judge for yourself (and sorry if that comment offends anyone -- I love C++ and use it every day). But you just can't beat the speed... Well-crafted C++ _should_ exceed the speed of even C (Why? Because templates...). As an aside, it's disingenuous to put Java in the same speed category as C/C++... The "fast" Java programs out there are basically C with Java wrappers (ducks thrown tomatoes). And just like C++, Java is very noisy (but for different reasons).
Python as we all know sort of takes the opposite approach, with dynamic typing a design-as-you-go mentality. And boy what a success it has been, with a flourishing package ecosystem. There's lots of good things to say about Python, but it's f*cking slow as hell (Cython is a hack, Numba shows promise, but PyPy isn't much faster... I was excited about Pyston but don't know where that went). It's not the fault of Python that it's slow -- it's the price of such a wonderfully dynamic language.
So enter things like Crystal. And trust me -- it's definitely early days with this language. But I like the fact that the designers really seem to care about the things that (to most of us I think) matter.... Taking an idea in our brain and putting it (simply) down in code, and then having that code run quickly. Yay!
In this day and age where we are swamped with hype from all of these new languages, let's give praise where it's warranted -- to the people are out there that are trying to refine decades worth of thought and finally "get it right".
My hat is off to those people out there that are forging ahead with these types of projects. Don't mind the criticism -- keep it up and great job.