Ironically my favorite AG's have some pretty sub-par endings.
WORST:
Curse of Monkey Island: Sure the plot worked out to a satisfying conclusion, but I was so disappointed with how short it was. They could have stretched it out a lot longer than that.
Toonstruck: It ended on a cliffhanger! And there's never ever going to be a sequel! It's the worst ending a player could encounter.
BEST:
Um.. this is going to be tough.. but I guess--
Monkey Island 1 and 4: Ended on a funny note. Was pretty satisfying. ESPECIALLY MI4 where
Spoiler:Elaine and Guybrush hand over governship to the Hermit. That's a guaranteed promise that if they ever make a MI5, there's not going to be any more boring legal adventures. WOOHOO!
What more could I want?