Special mention goes to the Outbreak scenario. Every other stage has a traditional boss monster you have to kill. Outbreak's boss? A sea of zombies that literally flood the main street of Raccoon City. Solution? Activate a series of explosives and blow them all up. Your character's holy shit reaction afterwards is quite justified.
Decisions, Decisions with two special endings, featuring Kevin and Jim, and Mark and David, who all are resigned to their fates and decide to kick zombie ass.
Kevin readies his gun to face Thanatos, eager to finish the battle against him.
Mark and David fixes up a tank and decide to go all out on a zombie horde.
Special mention goes to Alyssa and Yoko's special ending, where it's implied that Yoko told Alyssa everything, prompting Alyssa to publish everything she's been told in an article before destroying her computer, and smiling with Yoko.
David saving a scientist by clocking a zombie with a pipe in the introduction to End of the Road.
In the same scenario, Carter utilizes Mr. X as your protector! Just watching him beat up the hunters with no effort is enough to make any Resident Evil/Biohazard fan smiling.
In Desperate Times, a massive amount of zombies invade the police station and you are forced to defend it. Now, if you're playing online with 4 survivors on your group at the most difficult mode available, then get ready for one of the most thrilling experiences of the game.