Final Level: Malachor V
Why It Sucked: For one thing, we never did get to meet Revan (the mysterious protagonist from the first KotOR), which would have been awesome. Practically nothing is resolved, and Kreia (who for some unknown reason is apparently omniscient) attempts to wrap up every loose end from this 30+ hour game with a brief conversation.
How We Would End It: It's a well known fact that KotOR II was rushed out the gate, and Obsidian should have had at least another few months to wrap its enormous story up in a more satisfactory way. Too many of those loose ends—including the fates of most of the characters—are left dangling.