How about Advent of Code? They start out easy, but after a while the difficulty is all over the place, and it'll force you to seek out new features of the language. It's a somewhat "realistic" way to learn the language, instead of having a set of more contrived set of exercises that only make you look at a particular part of the language.

The first day, for example, will kind of force you to figure out how to parse arguments, how to loop, how to convert strings into ASCII... all basic, practical tools that you will need sooner or later anyway. Now it's your job to pick up a Rust reference, look around for the tools that you need, and use them to solve an actual problem.

That's how I got very comfortable with D.

http://jordi.inversethought.com/blog/advent-of-d/

If you do this for Rust, I'd love to see a blog post like the above.