I've beat it on Regular AND Veteran difficulties now. Regular was ok, but Veteran was a BEAR!
The number of times I had to replay some segments isn't EVEN funny! Been trying my hand at the Spec Ops missions, and I've got Alpha through Charlie unlocked so far. Got my brother to bring his controller over twice so far, and we've done some split-screen Spec Ops missions. VERY COOL! 
We both had a blast, and even tried some Nazi Zombies from COD: World at War.I read something in the newest X-Box Magazine that I didn't know about, and thought I'd pass it along. Those of you that have finished the Campaign (on any Difficulty Level), probably know you've unlocked the "Museum" level in the Campaign menu. It's like the Museum you see in the end credits, with a few differences. One gallery is all vehicles, which you can't do anything with. The other two have displays featuring scenes from the game, all with a mix of friends and foes, with a few neutrals thrown in. Also, there's glass display cabinets of many of the various weapons you get to use throughout the game. From pistols, shotguns, SMGs, assault rifles, sniper rifles, LMGs, RPGs, and even the Javelin and Stinger. While you can pick up and fire everything, the Javelin and Stinger require a "Lock-On", which you can't achieve, so there's no point picking them up. There's also an ammo resupply crate in each gallery also.
WHAT am I getting at?
Well, you may notice you can shoot and kill pretty much everyone, and they don't shoot back. There's a generator or two you can shoot, which will make it explode also. The two frogmen from the Oil Platform display I never could kill. Can't seem to bounce a grenade in there with them!
Anyway, there's an Information Desk at the front of each gallery, with a few potted plants and several computer monitors. Nestled in amongst this stuff, on the desk closest to the entrance, is a red bell. As you approach it, an orange icon appears over it, then the words "Do NOT press X" appear in the center of your screen.My advice is to get the M240 and maybe M4 MG, hit the ammo resupply crate, shoot off all the pots and monitors on the desks, resupply again . . . THEN ring the bell!
Another bit of advice: kill the dog, and maybe a few people BEFORE ringing the bell! You have NO allies once you ring the bell! Even though you've got "Friendlies" in the displays, once you hit the bell, they're your enemies, and they WILL frag you!
You don't get any points for doing it, and it doesn't seem to unlock any achievement, but it's fun to experience anyway!Good Luck!
