Thank you @percysgrowroom and @plaka37 for your input,

wpForo has 5 forum layouts with 6 combination of color styles, that's 30 design combinations that comes by default. There is no other forum softwares allowing you such large flexibility in forum look and feel. And you can customize them very easily with colors selectors and custom CSS. 

I'd recommend the Simplified Layout of wpForo 3.0 if you want to look it as classic forum. This layout is very close to the classic forums design:

It's possible I just messed up somewhere along the way, because it just doesn't look great on my end. I think the mobile design needs some work too. For example how the user info looks all stacked (see img).