My first real job after I graduated from college involved a lot of R. It’s a very strange language, though there are some very cool things about it. It’s still really impressive to see packages like codetools which allow you to identify the closure variables used by a function (which can be used to great effect to export them to other process or machines for distributed computation). Some of the techniques we used for moving functions and data between machines would be challenging in most other languages. The C/C++ interop is pretty legit as well.
It is however, a very complicated language. It has two different non-interoperable object systems. Functions like read.table are like whole semantic pies by themselves. It’s been a while since I’ve written anything in R, but I suspect I would go a little nuts if I had to write a lot of it now.