Sorry for necropost but it just aired here a few days ago and I just saw the recording.
Very good finale, had some nice stuff in it and overall fitting end to the series. Loved having all the old characters back and especially liked seeing Rachel all grown up. Nice touch with seeing a wide shot of the Hospital at the end, have we ever seen that before?
Ultimately I'm happy with it, but it's going to be strange not seeing new ER episodes anymore. The shows been a bit part of my TV watching life and now it's gone.
However, as much as I liked the finale, it didn't punch me in the gut quite as much as the Special Retrospective episode did. I was bawling at the end of that.