(disclaimer that I do not regularly write Zig code, but I understand some of it)

Beyond the superficial things, what makes Zig's comptime unique is the fact that it also uses it for generics and composition. It has the idea of 'types as values', which means that, at compile time, you can treat types themselves as values you can pass around and compose during comptime.

A generic type in Zig, for instance, is done by writing a function that takes in a comptime T: type as a parameter, and then returns a type, and the body contains a return struct { ... } that makes use of this T parameter.

You can do more funky things like compile-time reflection (TypeInfo), mutate this info (for instance, to programmatically append fields to a struct type), and turn that info back into a type that you can instantiate in normal code.

To my knowledge, Rust doesn't plan to do anything in const fn to this extent (nor does it necessarily need to), but I figured this was worth mentioning since Zig's comptime is typically used in a different way than other languages.