Bloobish [comrade/them]

Yup, biggest thing is that their attack, though expected by quite a few powers, came out of left field and add in the rushing forward on armies still using cavalry units and the early massive land grab via Germany makes sense

What does it take to impress you? To what would you assign their disturbing success?

Meth chocolate, fascism, and taking on armies using WWI tech and tactics

This, the biggest mistake Germany made was interfering with dominant western European capital (i.e. the US, UK, and France). If they had just devoured the eastern European countries and fought Russia then capital would not have batted an eye.