I've been doing this race since 2008 and I love participating. It's a good race to do with friends or family. I like that included in your race is a ticket to the festival. The Columbia St Pats Festival is one of the largest events in our city. I like to go early before it gets crowded.
It's a fun race where people are encouraged to dress as a leprechaun and there's prizes for the best dressed. Also it's through a neighborhood so you have lots of encouragement with families coming out to cheer you on or even offer you a beer.
Cons: This is one of the largest races in Columbia so it can be pretty crowded but by the time you get to mile 1, the crowd thins out. There are lots of dogs and strollers that can be difficult to navigate. Also, since they added the 10k, there have been times when the water stops aren't always ready for the 5k runners. But for a 5k, you don't really need much water. Some years the weather can be rainy. In 2015 it poured down for most of the race, but some years you can have beautiful running weather.
The course is a little hilly but not too bad. The finish line can get crowded when people don't keep moving but there are lots of volunteers to hand out medals and water. Every year they tweak something but the course has been the same for the past few years.
Packet Pick up was at Whole Foods for the past couple years and that seems to work well. Volunteers are friendly and there is plenty of time to pick up your stuff.
I think this is a must-do if you live in the area but plan to have fun. You may not get a PR but you'll be entertained by the fun along the way.