[Ninth]

I like two kinds of endings: the open ended ones, and the climatic ones.

Open endings: Still Life, Syberia 1. Leaves the player with a kind of nostalgia.

Climax: Simon the Sorcerer, where after spending three quarter of the game in a non-linear, completely accessible world, you have to get through very small, original and self contained settings (I love the Alice in Wonderland interlude) before you finally arrive to the bad guy, and defeat him in one last puzzle.
Or Indiana Jones FoA, in the heart of Atlantis, which you've been looking for the entire game.
In both cases, the game leads the player toward the ending, which feels extremely rewarding.
And more important, you actually play the ending in these games, the same as in Monkey Island, of Kyrandia 2, etc... I don't like the ending to be one long unplayable cut-scene. Hell, I hate it.

So to answer the original question: I want the last puzzle to exist in the first place.