The academics, hands down. There isn't another school in the country where you will receive as much individual attention and freedom to pursue your interests.
The lack of outside voices coming in. Marlboro needs more lectures, concerts, and culture. Also, Marlboro needs more recognition by the academic community.
Yes, I've met some amazing people and expanded my intellectual horizons drastically, and I wouldn't trade those experiences for anything.
You might also consider Vassar College, NYU, American University, UMD