4. Homeworld: Cataclysm - Fighting the Bentusi
Considering the fact that I wrote an entire column based on this battle, it should almost go without saying that I was going to give it a spot on this list. An (almost) unwinnable battle, it pits your fleet of miners against a force of and nearly unstoppable trade ships belonging to the advanced Bentusi. What makes this mission really special is the way it uses the battle itself to heighten the intensity of the narrative going on at the same time.
You're not fighting the Bentusi arbitrarily; you need their help to defeat an alien infection that could threaten the entire galaxy if it's not contained. The Bentusi however, are intent on just getting the hell out of Dodge and warping away to another galaxy. The only obstacle in their way is you. Your fleet's commander, in turn, is resolved to stop them even it means sacrificing every single ship in your fleet to bring them back to their senses. Honestly, words alone cannot do justice to this battle and the best way I can really explain my love of it is to just tell you to watch it for yourself.