Some great picks; Nice to know most of you have such good taste!

I'm trying to remember older games just so I don't end up repeating too much...
XWA - When your home is taken over by the Imps and you're forced to flee to the
rebellion, and later when you find out Anton sold you out to the Imps. Bastards!
TIE Fighter - When Harkov makes you take out a minefield in a @#*%$& TIE Interceptor! (gitface!) And once you are assigned to Thrawn and are hunting down Zaarin. (Taste my missile boat!)
Dark Forces - The Arc Hammer level when the epic ass kicking iMUSE music kicks in. You know what I mean. (Seriously, why can't people write music for games like that any more?! Michael Land, Clint Bajakian and Peter McConnell were GODS of the iMUSE system in all early LEC games!)
Republic Commando - The ending. Seeeeeev! Why did they kill off Sev?! He was the best guy in the game!!
Day of the Tentacle - Back... to the MANSION!

Sanitarium - The whole game is just a huge mind****!
Command and Conquer - When you first start the game with the Act on Instinct track playing
Forgotten Worlds - First meeting the final boss
Bubble Bobble - One of the secret levels (It had really spooky music! I was like, 6, and it scarred me for live!

)
Midnight Resistance - Completing it the first time and then finding I didn't have enough keys to rescue all of my family!!

ChronoTrigger - Pretty much the whole game was a jumble of WTF?, OMG! and *sniff*
Full Throttle - The ending, the cavefish and the bunnies

Super Metroid - I don't need to say it! I'm just glad it wasn't just me... Awww...
Sonic 2 - The end song before the credits (Although the credits music rocks too)
Diablo - The Butcher

Doom - I went through all that and they still killed mah bunneh!!

StarCraft 1 - When you have to abandon Kerrigan! Damn you Mengsk!! Li'l Jimmy almost scored!
System Shock 1 and 2 - Both games build pretty intense atmospheres, but the Delacroix reveal in 2 and the first time you run into a Cortex Reaper in 1 are two of my

moments.
AvP - I was on the verge of ****ting myself pretty much through the whole Marine campaign!

Thief: When the Trickster and Viktoria take Garret's eye

*ugh!* It really galls that you have to work with her later on in the sequel too

I never finished Thief 2 tho'

MechWarrior 3 - Intro cutscene, where everything goes tits up straight away

Frickin' lasers!

Battlezone (The Activision one) - When you first get attacked by Furies