Two things. I found their administration to be very "Tufts" focused, as opposed to applicant focused. While many schools touted about the resources they have to get you through medical school and help you along the way, Tufts presentations seemed to be more about what applicants could do for themselves, leaving me wondering what kind of support they provide to their students.
The other thing was the personality of the students. Of the 5-10 students I interacted with on interview day, all said that they're favorite thing about Tufts was the P/F curriculum. While this in itself is a great opportunity, the reasons they gave were more about not having to focus on school, and one even said having more time to drink, as opposed to using that time for research, getting settled into a new place and home, etc. I guess I just didn't click with the vibes they were giving off as to their culture as a school.