Nim has actually decent type-system with support for algebraic data types and generics. Moreover, Nim is a much higher level language and doesn't sacrifice performance to do it.

In short, while Go has deliberately shunned all modern developments in PL design, Nim has embraced them. Also Nim has real macros, while Go does not.

It's clear to me that though immature, Nim is a much better and more expressive language than Go.