The organizers claimed that the Indianapolis Mini-Marathon is the largest in the country (30,000 for the half-marathon, 3,000 for the 5K). The course was flat and fast (only 83 feet of ascent total). There were more than enough stations for water and the organizers put a lot of work into making sure all the details were taken care of. The people along the route were incredibly friendly and the volunteers were nothing short of heroic. There was a great system for gear check-in and plenty of food and refreshments afterwards. It was kind of cool running around the Indianapolis 500 track. You only run on the actual track for a little while and then on the infield track for most of it, but the last part in front of the pits was awesome.
The main issues I had was that there were too many people. I spent the first ten miles just trying to get past people. I couldn't hit my stride and maintain it until after the 10 mile mark. At that point in time I was way off my race pace. All i could do was enjoy the scenery after that. Also, they put quarter mile marks the last mile which made it seem longer. It was a great mind f%$#. They don't take pictures of you crossing the finish line either. You get your post race pictures in the recovery area.
If you are from Indianapolis or anywhere near, you should do once for the experience. However, if you are going for a PR on a 13.1, look elsewhere. It is just too crowded unless you can get up front early or a pro slot.
I have to say the coolest part was when I was sitting in the recovery area and it was announced that a 9 year old girl finished the race. The results aren't posted yet, but everyone was cheering. All in all it was a positive experience.