Some big differences in student life include the party culture: It will be more varied at Michigan (big school, so many different groups of people). It will be louder at Michigan (B1G major football school, very active Greek Life). Athletics will overall be a bigger part of the culture at Michigan.
Also, there will be a larger range and magnitude of student organizations at Michigan, and (in many cases) more members in these student organizations. At Wesleyan, you will know more of the student body, and anonymity will be less of a thing.