I have run this race 6 times and every year it gets better. Definitely one to add to your race list if you are looking for a well supported marathon. The entire city comes alive for the entire weekend of this event.
Race weekend begins with the expo at McCormick Center. The organizers make it very easy to get to the location with various shuttles as well as discounted parking. The expo is huge and can be a bit overwhelming to a first timer. There are tons of vendors showcasing the latest running products as well as the leaders in running gear selling shoes, and Chicago Marathon themed apparel. (Nike is the corporate sponsor and offers a HUGE pop-up experience at the expo). There are quiet a few elites who run this course and the race organizers usually offer some sort of personal appearance by some of them at the expo. (Keep your eye on the expo schedule to find out info on great speakers)
Race day is very organized, but make sure you allow enough time to get through security and get to your corral. Corrals and the wave start make the start of the race very smooth, but the corrals are packed, so get there early if you want to meet friends or find a comfortable spot.
The course was well stocked with aid stations and amazing volunteers. You pay alot for this race, but once you see how well it is supported by the organizers you realize it is worth it.
The weather was perfect for the 2014 race which always means amazing crowd support. Since this course runs through the city neighborhoods it makes it easy for locals to come out and cheer runners. This year was no exception, the crowds were every where and sooo energetic.
The finish line chute is the perfect size, not too long, but enough room to not feel crowded. There is a ton of room near packet pick up for runners to stretch and relax a bit before meeting up with family/friends.
If you run this race, keep a few points in mind.
*Don't expect a fabulous race day shirt, they tend to be a good quality but nothing special.
*Don't expect to get cell service after the race, the lines are always jammed.
*Awesome course to run a PR, but weather is unpredictable.

Overall the best marathon in the Midwest, maybe in the USA.