Did the LOST finale leave a good taste in anyone's mouth? All I could was "2½ hours of friggin' clip show"?
My all-time favorite series finale was the last episode Star Trek: Enterprise, it had a fitting conclusion with the creation of the Federation that was a very satisfying conclusion.
Most critics will list the finale of Newhart near the top of the list, and if you had never seen an episode of the show, you should still able appreciate the flashback to the earlier The Bob Newhart Show.
My opinions of shows I watched regularly through their series finales…
Good finales:
Battlestar Galactica
Boston Legal
Newhart
Star Trek: Deep Space Nine
Star Trek: Enterprise
Okay finales:
Sex and the City
Sopranos
Stargate SG-1
Star Trek: Voyager
Utter crap:
Ally McBeal
Angel
Buffy the Vampire Slayer
The L-Word
M*A*S*H
Start Trek: The Next Generation
The X-Files
Wasn't supposed to be an ending, but strong anyway:
Jericho
The Unit
Wasn't supposed to be an ending, thus it made no sense:
Heroes
Stargate Atlantis
Star Trek: The Original Series
If you don't see your favorite show here, that means I simply didn't see it (either the show or the finale).