A list of the worst game endings:

http://www.computerandvideogames.com/article.php?id=153510

The recentness of Neverwinter Nights II is probably why it did not get included in this list. 

Game:  Rich graphics, exciting animated scenes using the real-time player rendering and high quality voice actors.  Lots and lots and lots and lots of monsters of a huge variety of types and capabilities.
End: Tedious fight against the end boss, and then a slideshow with a very flat voiceover by someone I suspect was one of the developers.

Can you say “We have to get this out the door, to Hell with the fancy ending!“