Speaking here
The comments suggest it was ok, but what’s the straight dope.
It’s fluent. The accent is perfect and if there are grammatical mistakes or non-native weirdisms, I can’t spot them.
Native German here. Almost fluent, but there are some instances of confusing the proper definite article and inserting English terms for German ones (manatees instead of Seekühe, for example). There’s also a noticeable English accent, but a slight one. You wouldn’t take him for a native speaker, but one who knew German since a long time, as it actually was the case.
Not native, but lived there for 10 years, and I found it impressive as hell. Unlike @EinsteinsHund, I would not have guessed he wasn’t native if I didn’t know better.
On a side note:
I just thought he was impersonating Falco. 
Wow, that is quite impressive. I had no idea he was that good. EinsteinsHund is right, the words he uses are a bit off sometimes (e.g., right at the beginning, when he talks about growing up in the countryside), but as a Southerner I would not have identified the accent as English, but rather vaguely Northern German. The way he pronounces “Jagd” as “Jacht”, for example.
Interesting. Sea cow is sometimes used for manatee even in English.
Non-native, but aren’t initial-s words like ‘sind’ supposed to be pronounced more like (as we’d spell in English) ‘zind’? That’s where I keep hearing his accent.
Very well done though, certainly better than me.
I know these speech patterns from my American friends who, like Philip, spent a year of their childhood in Germany. Even without knowing who he is, I’d have recognized him as an Anglophone pretty soon.
I don’t hear anything in his pronunciation of sind though. He’s saying it with a lenis-s which isn’t necessarily voiced.
I understand he was also fluent in French.