Since we are asked for subjective matters (what we don’t like for “serious work”).
Julia, as a langage, is targeted to and optimised for computational scripting. It’s like a more general-purpose Matlab (with much much better typing paradigm).
So, if what you want to do is putting a quick-and-dirty 500-line script together to calculate stuff (as a single file or jupyter notebook, etc.), your experience will be excellent.
You can consolidate those scripts into libraries but that’s where the experience begins to plummet a bit: the langage offers very little guarantees to the programmer and does not promote proper software architecture.
Practically it means most of the largish code you’ll see out there is a mess to maintain or fix. You typically need to know far more about the overall code to make a change anywhere than in langages like modern C++, Go or Rust for instance… Same thing goes with Python, even though tooling has helped enforcing good practices for maintainable code there (but it’s “ok” or “good” at most, not excellent).
Now if you feel outraged, read again: I am not saying it is impossible to make a big maintenable Julia code base. It is just made harder. Julia is like a hammer: if what you need is to put a few nails here and there, it is the perfect tool for the job, but as the number of nails and precision requirements increases, your life will be made easier if you use a nail gun (though, again, a hammer is not horrible).
So I would say Julia is perfectly ready for “serious” research work.
I would not be reimplementing an OpenFoam, Comsol, Gromacs or Gaussian in there though (which is another form of “serious”, i.e. consolidated research work). Again, this is not impossible, but reaching such reliable performance in Julia is tricky to start with and again Julia offers very little in terms of architecture and guarantees. As a program goes bigger and bigger in size, being able to look at just a couple functions at most to solve a problem while being sure it won’t adversely affect unrelated pieces of the program is important. If you only count on unit testing for that, your guarantee is only as good as your tests, unfortunately.