I think it's interesting that they never finished some of the interesting story developments used over the years. I realized watching the finale that Dr. Cox's second child is not going to have any story line, which is big because they definitely hinted that she was going to have some "problems" after needing surgery in the womb. Johnnie C. has a child with Down Syndrome IRL, so I thought it was going to be really interesting seeing that difficult situation portrayed.
Other not-resolved storylines include Nurse Shirley (supposedly the twin of Nurse Laverne?), the relationship between Sean and Kim, and whatever happened to every single character who showed up for a few episodes, especially JD's girlfriends.
Also, where was Doug the last few episodes? He's been in like 50 episodes, but nothing for the finale?
HALLWAY: The biggest surprise guest in the hallway had to be Dr. Miller (the bitchy surgeon) with short, black hair. Totally didn't recognize her until I re-watched it and paused the DVR. Also, they didn't show Jimmy "the overly touchy orderly" massaging Dr. Beardface's Beard Face in the hallway, but you could see it over JD's shoulder in a later shot. Hilarious.
I wished some guests would have been there, including Brendan Frazer as Dr. Cox's brother-in-law buddy, Michael J. Fox as Dr. Kevin Kasey, Heather Graham as Dr. Molly Clock, and Tara Reid as Jordan's sister Dani. Pretty much, if they were a major character for more than one episode, I wanted them to be there. (Except Courtney Cox)