No, it's a Democracy. (Well Constitutional Federal Republic but that's a subset of Democracy).

It's functionally a little Oligarchic. But thats mostly just because all to many people won't vote for someone unless they see a lot of commercials about them. The party system is just inherent to a Democracy, but write ins for anything but president are an option. And if the people like somebody that much they'd be able to get the electoral college in line soon enough.

However most Americans don't want to vote for Nader or wherever it is you like.