Moments in game that have dropped your jaw

[Red Pawn]

The main menu from Halo. Yes I know it's just a big thingy floating in space, but the sheer scale of the damn thing combined with the iconic opening chorus was AND IS STILL like a magnificent wall of awesome (in the literal sense) that wrests all other sensations from my body and has me gaping at the screen until O'Donnel's last breath fades out.
ALSO:
"... I chose something different. I chose the impossible. I chose... RAPTURE."
F*ckin' beautiful.

 

[TheBarefootBandit]

The explosion of Megaton in Fallout 3 if you're evil. My eyes nearly popped out my head.

 

[Et3rnalLegend64]

Yes, a thousand times yes. No other moment in gaming was ever so potent and suprising.

I'm not sure if I'd say surprising, but yes, certainly potent. It's one of those cutscenes that stands out so vividly in my memory that it's not even funny.

The fight against Yami in Okami.

That was a ridiculously grand boss fight, combined with a complete mindfuck

Spoiler

I came all this way to fight some evil cyborg baby seal thing?

Yami was cool, but he just sort of appeared, all they say is "Yeah, that guy's the Lord of Darkness... somehow, go fight him. But the music makes up for that.

When I played it I felt overwhelmed. Especially when he took my powers.

"How the fuck am I supposed to fight this thing?"

I loved that bossfight.

Ditto on that. After the cutscene where you're brought back to your full shining power, the music just tells you that you're ready to kick ass. Such an awesome game.

And now for a complete mood shift. The part in CoD4 where your character is dying from a nuclear explosion. And you have to play it. Damn if it doesn't hit you hard.

 

[JMan]

One time while playing GTA 4, I took the helicopter to the highest possible height, jumped out, and landed on top of an old lady. You couldn't possibly plan that.

 

[Madcat555]

MGS2:Sons of Liberty:

Spoiler

When it all hits the fan and you're running around dodging guards in the nude.
I'll never forget watching him do one handed cartwheels because his other hand was needed to keep things "under control" also, I was 12 when I played it and I almost lost my bladder control when the game told me to stop playing it or else.

 

[Casual Shinji]

I was actually rather stunned, when in Infamous.....

Spoiler

....Trish died.

I didn't see that coming at all and it severely tugged on my heartstring.

Another moment worth mentioning would be, when you enter the huge furnice in Resi 4. You pick up some ammo here and there and make you're way to the exit. Suddenly the gate opens and two el Gigantes enter and you're stuck with them in the furnice. That moment certainly shrunk my balls to the size of little raisans.

 

[Keepitclean]

the cutscene titled "monsters" in halo wars

 

[Jerich0]

the beginning of bioshock. i had already read Atlas Shrugged, and i was just nodding my head until the city came into view and dropped my damn jaw. i was like oh. my. gawd. also, the big plot twist (duh).

the ending of half-life 2 episode 2. pissed me the hell off. also, launching the garden gnome. YES I GOT THE ACHIEVEMENT!

when jack thompson was disbarred (not really part of a videogame, but still).

resident evil 5, when they shoved that thing down that dude's throat.

when i first found out i was the nerevarine in morrowind.

my first big team game on halo 1. i went on a warthog rampage and got an un freaking believable.

when i kicked this one ghost's ass on halo 3. i'll post the video clip on my file share. it was pretty badass.

 

[Cozzzy]

There's been loads of moments, but the one that comes to mind is in GTA:TLAD in that cutscene when the camera angle suddenly changes and shows full frontal nudity of a guy. Basically giving Jack Thompson the middle finger. Amazing. I litterally stared at the screen jaw dropped.

 

[Dr. Wily III]

Chrono Trigger had many, but the one in my mind is

Spoiler

where Chrono gets killed by Lavos

 

[SomethingUnrelated]

Fallout 3,whe I died at the end. That was a bad version of jaw dropping. Luckily Broken Steel saved the day though.

 

[Biek]

The good ending of InFamous.

 

[pepe456]

Most recent: Pretty much every Scarecrow appearance in Arkham Asylum.

Spoiler

Especially the last one where you at first think your PC is broken.
I think my jaw dropped at every twist in that one..