I tried the demo of Uncharted 2: Among Thieves on PSN. It's multiplayer only but is very generous with what you get to try out. There are four different modes and all of them were fun. My favorite being the co-op mode where you need to find treasure. It's like playing the actual game, except you've got two other players and need to work together to take out the bad guys and get past certain places. There's deathmatch in there too of course. The game looks fantastic and the multiplayer mode is excellent from what I've played.
I highly recommend downloading the demo. I'm sure it will be a purchase for most PS3 owners.
"Fortune hunter Nathan Drake returns in UNCHARTED 2: Among Thieves™, a pulse-pounding third-person action-adventure/shooter created by award-winning developer Naughty Dog. Down on his luck, Drake is lured back into the treacherous world of thieves and mercenary treasure-seekers he had sought to leave behind. When a mysterious artifact propels Drake on an expedition to find the legendary Himalayan valley of Shambhala, he finds himself embroiled in a dangerous game of cat-and-mouse against a fugitive war criminal who’s after more than just the fabled riches of the lost city. Caught in a web of deception and plunged into an increasingly deadly pursuit that tests the limits of his endurance, Drake will be forced to risk everything – but has his luck finally run out?"