I don't repeat many races, but this is the one I come back to every year. It's just such a great overall experience and a great summer race. The course is mainly on paved roads in a nice large park, through some neighborhoods to circle a huge lake, and then back to the start. It starts near the Baltimore Zoo, and the nice medal features a different zoo animal every year. Post-race features watermelon along with standard race fare, and parking and amenities are close by in the park. The swag/gear each year is fantastic. Instead of a simple race shirt it might be a rain jacket or a thick 1/2 zip pullover, stuff that has become staples in my running and everyday attire. This race is also part of the King Crab Challenge series of races that are fun and earn amazing swag for locals who are into that kinda thing.
It's actually hard to pick out any one aspect of the race that makes it so great, it's just an overall great experience that keeps me coming back every year.