The most notable distinguishing feature of the dialect is that the letters "o" and "u" are pronounced as centralized vowels ([ɵ] and [ʉ], which are also used in Swedish, for instance). Speakers of other German dialects that do not have these sounds tend to perceive these sounds as being "ö" [ø] and "ü" [y] respectively. For example, they hear [ʔæʉs] ‘out’ as if written "aüs" (Standard aus [ʔaʊs]) and [ˈʔɵːma] ‘grandma’ as if written "Öma" (Standard Oma [ˈʔoːma]). Front rounded vowels are pronounced as non-rounded ("ö" = [eː], "ü" = [iː]). Final -er is pronounced [ɝ], which speakers of other German dialects tend to hear as [oː]; e.g. [ˈheː(h)ɝ] ‘higher’ (Standard [ˈhøː(h)ɚ] höher) is misheard as if written "he(h)o."
Okay, this is all I need to know. It sounds awful.