To me, the uniqueness of Zig's comptime is a combination of two things:
1. comtpime replaces many other features that would be specialised in other languages with or without rich compile-time (or runtime) metaprogramming, and
2. comptime is referentially transparent [1], that makes it strictly "weaker" than AST macros, but simpler to understand; what's surprising is just how capable you can be with a comptime mechanism with access to introspection yet without the referentially opaque power of macros.
These two give Zig a unique combination of simplicity and power. We're used to seeing things like that in Scheme and other Lisps, but the approach in Zig is very different. The outcome isn't as general as in Lisp, but it's powerful enough while keeping code easier to understand.
You can like it or not, but it is very interesting and very novel (the novelty isn't in the feature itself, but in the place it has in the language). Languages with a novel design and approach that you can learn in a couple of days are quite rare.
[1]: In short, this means that you get no access to names or expressions, only the values they yield.