We got a few sneak peeks at the upcoming main adventure mode in Radio Cobalt, but rejoice: I bring ye fresh treasure! (oxeyegames.com)
That's pretty much the longest main adventure in Mario game history (not that there's much competition there, Mario games are usually quite short anyway) and it's only a best case scenario estimate. (gamingreinvented.com)
Infamous 2 has a solid gameplay and a complex main adventure. (metacritic.com)