Iterators were another one. The ability to express data transformation (mapps/filters/etc) in a very concise way blew me away. I had no idea what I had gotten used to in Go, though that's definitely not to say that I didn't feel the pain.
There's advanced features in Rust I could live without, but most of it just feels empowering. The beauty in it though, in my mind, is that you don't need to use all that advanced stuff. You can write Rust shockingly similar to Go.
The only thing Go truly nailed in my eyes is green threads. Those will always be better in Go than Rust (though futures are getting way better). Go nailed green threads.
But all the other "lack of features as a feature" left me frequently wanting for more tools to solve simple problems. And I was a Go nut. I have a Gopher plushie in my car for Petes sake.