The ‘Mats are definitely one of those sort of doomed, “shoulda been a contender ‘ma” type bands. Loved their stuff from the beginning till ‘pleased to meet you’. 
Bob Mould definitely worth seeing live. Husker Du are/were one of my favourite bands ever, although they’re not recognisable in a mainstream sense they definitely had a big influence (in certain circles) so I never quite think of them as being underrated. 
Mentioned Red on Green and I did have a bit of a re-listen to those Paisley Underground bands recently. Rain Parade in particular I liked a bit. 
As you mentioned Big Black I thought I’d post Cardiff’s own answer (Slowjam): 
https://youtu.be/QzA19BnsdGE