1. A "better C" in the sense that the language core of Zig fixes the commonly known and accepted design warts of C which are hard to fix because of backward compatibility requirements - this part is actually less complex and easier to learn than C because there's less implicit and less unexpected hidden behaviour while having roughly the same "language surface". If you are used to C's somewhat sloppy "hippie-approach" to programming, be prepared that the Zig compiler will yell at you a lot at the start of the learning phase, especially when it comes to implicit type conversions which follow very strict rules in Zig (when compared to C).
2. A much richer and actually useful stdlib (in this area Zig is also a much better C++), don't quite expect a Python-style "batteries included" stdlib though.
3. A much more complete compiler toolchain package, with a build system, package manager, C/C++/ObjC integration and cross-compilation to the important target platforms included and working out of the box (and most of that integrated into the Zig executable, a vanilla Zig install actually only has a single executable, the Zig compiler).
4. And finally the "visionary part", where Zig differs most from C and other languages and explores its own path, like the approach to comptime, generics, type reflection and error handling.