I long ago stopped watching ER, but for years it was appointment TV for me. I loved that it was set in Chicago and would enjoy listening in for the "Chicago" things. (My favorite was the mention of the piano store near the expressway. They got the location wrong, but it was too funny when it was dropped in.)
The Tribune has a good article about ER and it's ties to Chicago. I still remember walking out of class and seeing Clooney filming by the restaurant (long gone now) near Hilton off Michigan Ave. And the day we saw a bunch of cast members filming near the bridge.
I'll be watching the finale on Thursday because it seems like the right thing to do. It's also sad that it is the end of an era for not only the show but programming at 9pm. In the fall, I WILL NOT be watching Leno.