Anyone else try this? The museum goes insane and all the dudes start shooting you. I killed em all and then saw it reset, which was really creepy because it was so quiet.... Kinda cool, and kinda weird to be able to gun down Price and Soap and all the others.
 
So yeah, if you've beaten the game and haven't gone into the museum yet, go there, go pick out a gun, and press the button.
 
EDIT: And yeah, I heard about it on the MW2 Bombcast.

I pressed the button and went "aaarg" storming out of there like a regular Han Solo. 
Then I took them down and then went to the other room with dudes and pressed the button there and gunned those dudes down too. 
Then I made them all Reset, ran into both rooms, pressed the buttons and ran into the middle room with the helicopters and tanks and stuff and tried taking them down.. That didn't go all too well :P

Very hard to do especially on veteran. Good to have either the AUG or the AK with the thermal scope and the M79 Thumper.

I pressed the button but since the game was on veteran difficulty I died instantaneously.

I only left one guy left, and then pressed the button. I figured that it would bring everyone to life to kill me, and I was right.

That level is not easy. Really interesting idea by Infinity Ward.

" do you get any reward for beating it? "

I wasn't sure what was going to happen. I thought maybe a nuke would go off and kill me but no, just everything else killed me. I was pretty surprised.

That level was really odd being able to kill Soap, and others. Like the person above said, I shot everyone before pressing the button except General Shepard who I left alive until he charged and I emptied a full AA-12 clip into him. That felt really good for some reason.

I was doing really good blasting everyone away, but then suddenly Price was up in my face and he beat me down. 

I spent a good 15 minutes seeing how many of the frozen guys I could kill with a flash-bang

" except General Shepard who I left alive until he charged and I emptied a full AA-12 clip into him. That felt really good for some reason. "

Hoooooly spoilers!
 
Edit: NVM, noticed the title.

First time I did it I didn't walk around to notice the stash of guns, so I thought it was some crazy hard extra level or something (almost cleared the one room w/ just pistol).

The Only way i killed everyone was with the Riot shield. Without it, on Veteran that Juggernaut would eat you alive.

missed opportunity,  should've gotten a trophy/achivement for taking out the museum haha