I disagree; you can learn 90% of Go in an afternoon. However, you also do have a point; the power of Go is not apparent in an afternoon, but in longer term and larger projects spanning years or decades, and hundreds or thousands of developers. It was made by and for Google to solve Google's problems, which include millions of LOC written and read by thousands of engineers over the span of decades.

So while at first you think "eww, err != nil everywhere", at least in a decade of reading your own or someone elses' code you'll know exactly what's going on.

How many languages are similar? I feel like a lot of languages in the past decade have had a steady migration in things like error handling, so 10 year old Java code is incomparable to today's Java. Whether that's a good thing (the language has evolved and is now more ergonomic) or a bad thing (I no longer know what's going on here) is the big debate.