Froman summed it up pretty well, but I tend to be a bit more positive about the John Muir trails. Yep, theres the limestone grids and plastic crap in spots, but the trails have a pretty good if somewhat tricky flow (not tech flow, but momentum flow) and theres some short, steep climbs that will keep you honest. The best part about them is that you can get a good bit of mileage, its a great spot for building fitness. The 'connector' (to emma carlin trails) was fun last time I rode there, but I thought the "trail maint." in Emma Carlin trails was lamer than John Muir...almost pavement in spots, but that was 7-8 years ago, so that could have changed.
If you ever had the slightest inclination to buy a SS or 29er HT, or a SS/29/HT, the midwest riding woud be a great reason....then you can bring the hurt when you you come back to CO next summer.
Don't forget about Challenge Park Extreme (!) in Joliet, that could be good times on the Intense.
http://www.cpxsports.com/index.php