For me,on both accounts,it's an "Awesome game becomes FUCKING ACES!" moment.
Who here played Supreme Commander,and it's expansion Forged Alliance? I have. They. Were. Awesome. So,original SupCom. Final mission for all sides,but special mention goes to the UEF version. Let me set the stage. Supreme Commander is a large scale science fiction RTS where you must build a base and produce a MASSIVE army to get anything done in a war that has spanned over a thousand years over hundreds of worlds. This mission,for all sides,is the battle for the Black Sun Superweapon on Hawaii. Black Sun was developed by the United Earth Federation as a means to end the Infinite War by using the game's FTL technology (Quantum Gates;think man-made Mass Relays) to deliver a planet obliterating energy beam to the core worlds of their enemies,the Aeon Illuminate and the Cybran Nation. Throughout the course of the game,which probably takes place over the course of months,if not weeks,the UEF was losing grounds as they focused all of their efforts to the development and deployment of Black Sun.
And so that brings us back to this mission. It takes place on Earth,which has been under siege since the beginning. The UEF are trying to defend Black Sun from their enemies,who have managed to establish bases mere kilometers to the North,Southeast,and Northwest of Black Sun's position. In the UEF campaign,you have to simultaneously defend Black Sun,your base around it,and then destroy the surrounding enemy bases,although only the one to the Southeast needs to get destroyed. During this time you're under constant attack by enemy air and navy,with occasional Experimental (think mobile superweapons) units coming in as well. Your goal as the UEF? Stop. Them. Dead. If you get the chance to play the mission,it's pretty damn awesome. As the Cybran,your sole goal is to capture Black Sun,and as Aeon you need to destroy the OTHER Aeon base (Infighting borne of religious doctrine) and capture Black Sun. What made this an improving moment? The sheer GRAVITY of it. This is the only mission,for any side,where you're given full access to your faction's arsenal. Before now,you couldn't build Experimentals. Now? You get all three. And then there's the tooltip for the activation of Black Sun. "End the Infinite War."
In the expansion,Forged Alliance,the moment comes MUCH earlier. First mission,in fact. The scene? A secret base,assaulted by a genocidal alien menace. It was supposed to be staffed by the best,using only the best tech. And they're getting CURBSTOMPED. Your mission? Bail them out. You arrive at an outpost as your door in is being destroyed,and it's your job to build a new base,from the ground up,to destroy a fully developed alien base producing their own Experimentals to save not only the base you're here to bail out,but also a nearby city. It just sets the tone for the entire campaign. Oh,and the aliens are backed up by crazy cultists with artillery and all-round better toys than you. Best part of the game? The final mission takes place on the exact same place the main game's final mission took place.