If you're fast and you live in Chicago, then you do this race. It sells out in less than a half an hour, at 6:30am on New Year's Eve, and there's a reason why. Hands down this is one of the best organized half marathons I have ever completed, ever.
The weather is always questionable (rain, snow, wind, ice, etc), and the course is hilly and pretty tough. The aid stations are plentiful and very well-staffed. The volunteers are enthusiastic. Having the high school open before the race (RE: indoor gear check and toilets) is really an advantage. There are only giant pretzels and Gatorade at the finish. Medals and shirts are always fantastic. This is a really great race, definitely worth getting up early to register!