I'd say if you are someone who's even remotely mathematically minded, learning to use Mathematica is an extremely useful experience. As an example that recently happened to me, while doing front end work I needed to construct certain geometric figures as an SVG polygon; I used Mathematica's built in graphics primitives combined with its plotting capabilities to find the polygon in no time. Even though the end result is a piece of JavaScript, Mathematica gives me a way to prototype the whole thing in an environment that's "batteries included" and well-polished.
Mathematica is way more targeted to the "general public" though. It's fairly obvious that MATLAB started its life as fronted to FORTRAN.
I second that and there are quite a number of scientists which use MATLAB and FORTRAN side by side.
I would extend this statement: MATLAB feels like a REPL to FORTRAN while Mathematica like a REPL/library to/for LISP.
Actually, it's way more targeted to mathematicians. The level of symbolic computation it can do is way ahead of any symbolic toolbox you'll find. When I was in grad school, I used NumPy and my group mate used Mathematica. One day I was looking up identities in Gradshteyn and Ryzhik (a bible for identities), and he asked why I bother as Mathematica had it all. He challenged me to find any identity that Mathematica couldn't handle. I thought this would be easy as G&R has more stuff than any other identity handbook out there, but I lost the challenge.
[0]: http://maxima.sourceforge.net/ [1]: https://wxmaxima-developers.github.io/wxmaxima/
A large OSS player is nowadays also SageMath https://www.sagemath.org/ which is a kind-of-meta CAS which can actually proxy evaluations to Mathematica, Maxima, Octave and many others, in a more or less uniform pythonic notation.
Probably needless to say, when it comes to evaluation power (for instance for integral solving), Mathematica is unrivalled from OSS projects. However, in certain fields (such as number theory for SageMath or the overall web notebook infrastructure by the IPython and Jupyter projects), the concurrency is catching up or may already have overtaken Wolfram's products.
So, one can say it is as closed to Mathematica as MATLAB is.