"all ghuilled up" i think that's what it's called. It's the flashback mission before the other one "One Shot, One Kill" where you play as captain price in both when he was a Lt. at least i think he was a lieutenant.
I don't actually own the game, but I watched a friend play it and I'd have to say my favorite level is either "All Ghillied Up" or the one where you fly around at night in a C-130 gunship and take out ground targets using thermal vision.
Singleplayer: "All Ghilied UP" - I love sniping ingame, so how can not love this level?
"Death from above" - Woah!I see little pieces down there! Awesome level.. It kind makes you feel like god, blasting those guys with huge, huge bullets.
Multiplayer "Crash" Well designed for bother sniping and more open combat.
"Shipment" - Ever had a knife only fight on this map? Awesomeness!