Parliamentary debate's most distinguishing characteristic is that it is impromptu. When we go to a tournament we have no idea what the topics we will be debating are. We do not spend our entire lives in the library researching the same topic repeatedly. Rather than debating whether the speed limit should be set at 55 miles per hour for an entir year, the topics you can bring in are considerably more varied. They range from making mandatory dress codes in schools to the benefits of natural grass versus artificial turf to the viability of the Force as a major world religion.
Parliamentary debate is fun.
For more specific details check out Bobby's Guide to Debate .