Hypothetical: Final mission, play as all three main races, enemy is a Protoss-Zerg hybrid faction that would have been a fun addition to the multiplayer as a fourth race (think Naga in Warcraft 3 TFT).
The mission will get universal hate because controlling three races as at once is damn difficult, and because the dialogue is so cheesy people puke when they hear it..
I'd expect something more akin to Twilight of the Gods from WC3.