Historically, it was designed to resemble C#, yet transpile to GNOME-like GObject-based C code, to provide an alternative way for GNOME developers to get higher level language syntax without having to depend on Mono/C# (which was very controversial at the time).
So the biggest difference from C# or Java is that there is no VM. It is mostly syntactic sugar over C and GObject.
At least, this was the case last I paid attention 15 years ago.
I think I got in a rabbit-hole with it around 2010 for the same reason of liking C# but not liking who backs C#, but I already had enough not marketable languages
> but I already had enough not marketable languages
Ha! Ain't that the truth :-)
It touches on a big problem for new language development in that there are barriers to entry at getting workable in a new language, but employers don't want to use them unless they can hire for them, and they can't hire for them unless people use them, but people don't use them because they can't get hire'd to use them, rinse and repeat.
When I tried it many years ago it was a really leaky abstraction over GObject and C. If you didn't understand exactly how it worked under the hood, stuff would segfault on you pretty regularly. But I suppose that's par for the course in the GObject universe.
I actually first heard of Vala just a few days ago when I was looking at a C#-related PR[1] for highlight.js:
> This fails the tests as the Vala default.txt is recognized now as C#. However, Vala is very close in syntax to C#, and the default.txt also seems to be valid C# so not sure what to do about this.
So the biggest difference from C# or Java is that there is no VM. It is mostly syntactic sugar over C and GObject.
At least, this was the case last I paid attention 15 years ago.