These are pretty big to me:

The garbage collector is now concurrent and provides dramatically lower pause times by running, when possible, in parallel with other goroutines.

By default, Go programs run with GOMAXPROCS set to the number of cores available; in prior releases it defaulted to 1.

But how important is this? It doesn't seem like it affects the average user:

The compiler and runtime are now written entirely in Go (with a little assembler). C is no longer involved in the implementation, and so the C compiler that was once necessary for building the distribution is gone.