Sorry for this general question but to be honest I hate more and more coding in TeX and even if I am a very beginner coder in LaTeX3, I really appreciate using it.
Strictly speaking, as mentioned in the comments, LaTeX3 is a superset of TeX. So, if there is some capability that TeX provides, it will also be available in LaTeX3.
The LaTeX3 programming syntax is an attempt at making many aspects of TeX programming more regularized and predictable. TeX is, as you've noticed, very much an island unto itself in its programming style (I would say that its closest non-TeX analogue would be the C Prepreprocessor and the latter, being non–Turing complete is less capable than TeX's macro language). LaTeX3 attempts to establish conventions for naming and syntax that allow for greater expressiveness in programming while retaining TeX's power. The comments on the question give some good examples.