Today, I'd like to introduce a concept of video games I call "middle finger endings." That's my totally non-scientific term for when a still photograph of the scenario writer (or antagonist's voice actor, depending on the game's age) giving you, the player, the middle finger while the credits roll would have been a more emotionally satisfying ending than what made it to the disc. To qualify as a middle finger ending, the game has to have been enjoyable on some other merits, and just... fall apart when it comes to wrapping the plot up.
My nomination: Inca II: Wiracocha (released elsewhere as Inca II: Nations of Immortality.) It's an oldie, but for the most part, a goodie- half Sierra adventure game, half space simulator, half movie (three halves?!) It had a great plot, well-written characters (dialogue's a little clunky, but it was originally in French, so it gets a pass there.), awesome soundtrack (especially the space combat song, Tumi.), tough puzzles, it had everything I loved about Sierra gaming as a child.
Then... the ending, such as it was. Maybe it's the fact that I downloaded the floppy disk version instead of the (far superior) CD-ROM version. Maybe something was direly lost in translation from the French. Maybe I missed some plot points. Instead of watching the villain die in an asteroid fire, my Incan gold spaceship rocketing away to planet Cuzco to meet up with my '30s fighter pilot-dressed Han Solo clone buddy (If anybody from Coktel Vision is reading this, make an Inca spinoff about Kelt! He was awesome in Inca II!) I get... text.
More specificially, THIS. This resolves nothing. Did I live, or did I die placing the last Great Inca Power in the asteroid? What about the bad guy, Aguirre? What about the traitor in my midst who spurred my son to his death, starting this whole mess? Is my son Atahualpa dead or resurrected?! Was the asteroid Wiracocha, coming for His three Great Powers?! Are El Dorado (me) and Aguirre (bad guy) now the same person!? WHAT THE HELL JUST HAPPENED?!
A still picture of Ivan Bond (Aguirre's motion capture actor, and I believe voice actor in the CD version) flipping off the camera would have been more plot-conclusive! I guess Coktel ran out of money and said, "If you want an actual ending, go buy the CD-ROM version, only $59.95 at your local software store, as recently as 1993."
So! Sorry for the rant! Post your worst video game endings and your thoughts on them here!