I wonder, how did you folks react to seeing it when you did? (I assume many of you saw it when it originally aired) Also, any other similar feelings from anything else?
I watched the show when it was first airing, as a kid, and then the reruns into college in the 80's and 90's.
There are some pivotal TV moments in MASH. That last episode had a few: Hawkeye admitting/realizing that the rooster the woman killed was her child, and then the 'Goodbye' written in the rocks. I wouldn't be surprised if it was on the top 10 list of all time TV episodes.
The other one that got me was when they killed Henry Blake. It was completely unexpected, and when they interviewed the cast and writers, it was apparently kept a secret from all of them as well, up until shooting. That was the first time I saw a 'beloved' TV character get killed.
A similiar, though less poignant feeling, was the finale of Cheers, as I watched every episode of that. It marked an era in time that I was saying goodbye to. I was in college when it ended. So, it didn't have emotional impact that the MASH finale had, but it felt like I was losing some pals.
There have been some stellar episodes of shows too. The Miami Vice episode "Out Where the Buses Don't Run" is simply awesome. If you watch one episode, watch that one.

Or Magnum, PI "Did You See the Sun Rise?"