Heh. I lived in Columbus, and to give my own advice:
1) The Columbus Zoo is not all that. Someone in this thread said it was 'one of the best in the country'. I certainly hope it's not, because it's not all that good, IMO.
2) COSI, when I went there, was extremely interesting. I was, however, in third grade, and I don't know how many 'adult-oriented' activities they have there.
3) OSU is a rather normal (albeit large) university. You won't really get proper exposure to the 'feel' of it, though, during summer quarter.
4) On a church front, may I suggest that you may want to see the beautiful orthodox cathedral on High St. literally about 2 blocks from the Convention Center? Quite nice, all told. You may also want to check out St.Patrick's, a Catholic church directly east of the Convention Center. Rather small, but probably the most traditional church I know of, offhand.
5) Branching out a bit, I saw the Tecumseh drama, and wasn't all that thrilled by it. If you want to see Native American stuff, the Great Serpent Mound is quite interesting.
6) When I lived around Dayton (an entirely different time period from when I lived in Columbus), I enjoyed hiking in the Greater and Lesser Miami river valleys. You might want to consider that. Very restful.