One behavior I like about Matlab is that functions are functions. Arguments are passed by value and there's no way a function can modify its arguments (well, except perhaps objects which are less common).

Matlab will try to optimize and avoid a copy if the function does not modify the argument. Matlab is also (sometimes) smart enough so that A=f(A) will modify A in place instead of making a copy.

This is what I expect from a math oriented language. Maintain the illusion of referential transparency but optimize under the hood if possible.

Also Matlab has a reasonable JIT compiler. And a good debugger.

I no longer use Matlab but it is a very productive environment for scientific computing (simulations, exploration).