The Keys 100 was one of my best performances as an ultra runner, so naturally I'm going to think highly of this race :)
The course is mostly beautiful, with the ocean in view for much of the race. A few times you get into cities and neighborhoods, but overall it's running along the coast.
It's hot. It's humid. Don't show up with a heat plan, because you'll struggle unless you have a way to get plenty of ice and water along the course.
The finish line party is the best of any race I've ever done. Beers, BBQ, Pizza go along with live music and a party under a big tent.
Highly recommend coming out for one of the many distances for this event!