For me, the best series by far that Dan Carlin did was the one on Genghis Khan ("The Wrath of the Khans", I believe it's called). The WWI one was also quite engaging, though. Before hearing it, I really was not interested in WWI at all, but he managed to make it very interesting for me.

I have listened, and you're right that they're amazing. Perhaps OP is right that they would be better printed, but I doubt it, Carlin does speak with a passion.

In my defense, i did use the weasel word "mostly" :)