I travel to and through ORD a lot, many times per year. Of all the major Untied Hubs, ORD has done the best job upgrading their clubs. EWR has a lot of catching up to do, which as my home airport, I'm excited to see some sort of movement.
ORD clubs have the newer look, newer food choices, bigger bathrooms and lots of locations.
The thing is, when I fly internationally, I will always choose the international airline club (Luftansa and SAS for examples) over the American clubs because they have a much more hospitable nature.
But for the domestic flights, and especially when routing through ORD, which let's it, doesn't always have the best weather and delays are common, this is a great escape from the crowded airport.