Methodists are a little more traditional in their ceremonies (communion, reciting the Lord's prayer, etc.), but the belief system is the same. Baptisms are similar, but with the same ceremonious differences (Methodism being more formal than non-denominationalism)
It's really just a question of formalities
Methodist churches are a part of an international organization. Interdenominational churches are independent and try to avoid taking stands that alienate any Christian.