Yes, function call polymorphism. Especially combined with Mathematica's piecewise syntax. I didn't really use it for numerics, it was more for Lisp/Prolog type things. I was always impressed at how short and readable the Mathematica code ended up being. I used to use Mathematica quite a bit to generate C++ functions.

But it's a very different use case than Matlab. One of the things I like about python is it isn't too bad for sliding between lispy/functional modes for some things and more lapacky things elsewhere. Matlab has a better syntax for the lapack parts but trying to do anything functional gets really annoying and very, very slow. But still I would say Mathematica has the best pure math syntax for those sorts of things. I don't have any experience with sympy, I should probably check it out.

Mathematica is nothing less than a work of art. I dedicated a fair amount of time to become proficient, but it never solved the use case I had (find derivatives for complicated functions- this was before autodiff was common).

Unfortunately, Wolfram himself has made a number of decisions that greatly limited its applicability and so it will always be niche.