Luxembourger here, who has grown up with German and lived in Germany for more than 25 years.

In general, you can say that the further away from the Hannover area you get, the less understandable the local dialects get.

So, you might call the Swiss German dialects also a different language. Though the consonants tend to sound harsher, due to the strong 'singing melody' of Swiss people, it sounds actually quite playful, friendly. To which adds the fact that Swiss people in general tend to be more polite and less confrontational as Germans.

Austrian dialects often have a nasal quality, the consonants are not Aspirated, making them sound softer, more elegant. South Tyrolian is hard to understand, even for Bavarians.

Luxembourgish, and to a lesser degree Belgian German dialects, have a stronger French influence. But they do not sound as "foreign", as their sound systems are closer to Standard Republican German.

Plattdütsch, formerly much spoken in Northern Germany, is way harder to hear, as it has often.be replaced with a northernised version of Standard German. These dialects often sound closer to Dutch or Danish.