I haven't actually seen the last 7 years of ER, so I missed a lot. The last episode I've seen was from the end of the eight season (where Marc died).
But I still wanted to see the last episode. And many claimed that it was a homage to the pilot "24 Hours", so I watched that first.
And I have to say it were great 3 hours. To see how it all started and then to see it 16 years later and how few has really changed and how the people have developed. Of course I didn't understand all developments due to that 7-year-gap and I missed a few of the people (Romano, Kovac and others) but it was still a great ending. The show has come to an end but life goes on in that fictional universe. That's my kind of series finale.
And there actually were many parallels to the pilot, like Lydia waking the current attending or the new med students (16 years ago: John Carter, now: Marc Greene's daughter Rachel) and other small yet noticeable things.
It was a great end to a great show and I am sure some day I will watch the missing seasons.