(Their intersection of uses isn't total, of course; Python's still got Go handily beat for numpy-ish stuff and interactive use. See Julia for a possibly-superior post-90s competitor in those areas, though I've only played with it.)
But that's not to say it doesn't include good stuff.
I'd say support for lightweight threading, CSP (channels), structural typing, fully embracing first-class functions (crippled python lambda, anyone?), and a build-system integrated into the language rather than left to 3rd-party-tools are all distinctly post-90s features, for a mainstream language.
Also, gofmt is a huge boon. The Go community focuses on ecosystem and ergonomic human factors of development feels distinctly post-90s-lanauge to me.
Also, the 90s saw an intense, misguided focus on "object-oriented-programming", which Go completely, mercifully ditches. In that sense, it's post-90s. :)
(Well, OK, maybe OO-style programming is good for UIs -- thinking of stuff like iOS/Cocoa apis and Unity.)
This definitely should not be interpreted as a slight on Go, many people would very happily trade that lack of benefits to get that lack of drawbacks.