Hmm...I understand scholars tend to classify only 9 main Chinese *dialects, but within these 9 main dialects are subsets. No, I'm not a linguist, but I've studied linguistics and still keep my interest in this area.
The northern Chinese would sound pretty similar to Mandarin (depending on how close the dialects are to each other). Even Beijing has its own dialect, similar to Mandarin. What we call Hockchew is actually Northern Min.
Dialects even cross provincial boundaries. Southern Min is spoken by people in both Fujian (Hokkien) and Guangdong (Canton) provinces.
Anything else you want to know? My 2+ years in Shanghai has been very fruitful
*Linguists would call them "languages", as true dialects should be mutually intelligible, which the Chinese ones are not. Examples of dialects include Teochew-Hokkien, which comes under South Min dialects. Another example would be Southern American-Black Vernacular American, which again are mutually intelligible, even though there are substantial differences. Even Chaozhou Min and Shantou (Swatow) Min are actually dialects of each other, with some differences. Even Shanghai itself has 3 dialect subsets - Chongming Shanghainese, city Shanghainese and rural Shanghainese (those spoken by Qingpu, for example).