Would a Multiparty Democracy Be Better?

What are the advantages and disadvantages of a two party or multiparty system for democracy? Could the US ever see a successful third party (or even more than three parties)? Why or why not? How would a system with more parties work with the US constitution? These questions and more will be considered in a context of comparisons with other countries around the world. The presentation will be brief, in order to allow extensive facilitated discussion on these matters.