The Crichton estate doesn't have a patent on hospital shows or on Noah Wylie playing a doctor. Pretty much every hospital drama has the same format of doctors and nurses and interns all dealing with emergencies and life or death situations.
I fully give them that they talked with the Crichton estate about an "ER" reboot but it didn't work out so they went back to the drawing board and created something different. Of note, the "Deadwood" creator David Milch had originally wanted to do a show about the Roman empire but HBO already had "Rome" so instead he re-tooled it into a Western. It'd be like if the creators of "Rome" sued him over it. Things can start out as one idea but end up as something completely different and "The Pitt" feels very different from "ER" to me.
ETA: Shawn Hatosy (sp?) is also in the show as a wild card doctor who may or may not be the sanest person. He starred in another John Wells show as an unhinged character before but "The Pitt" is definitely not a reboot of "Animal Kingdom" despite having the same creator or actor. I think Wells just has certain people he really loves working with.
