This is a medical drama that seems to have captured the imagination so much more than any other before it. You really identify with the characters, and yet every time it risks degenerating into soap opera, you get a face full of standalone medical drama to bring you back to "real life".
I thought the last episode excelled in the way in which it brought everything to a close and yet left a positive note for the future. The programme is gone, but the hospital carries on and we still identify with it and wish it well. They even resolved all the subplots, something totally unheard of in an ER season finale.
A nice, albeit predictable, touch that the old stagers were brought back in one by one over the course of the last series - and probably right that for most of the time, they were just there for our benefit and did not interfere with the "real" story of the hospital itself. Particularly nice touch that they used the same actors for the two children who returned (Rachel Greene and Reese Benton).
The episode wallowed a little in sentimentality, because the expectation was that the audience would welcome that, but again, the usual side stories were juxtaposed with hard hitting, fast moving, medical action - something that was always a strong point of the series.
A final nice touch for me was the return to the old theme music. A tacit acknowledgement perhaps of how much everyone hated its replacement?