I picked up Demon's Souls, a PS3 Exclusive, and man this game has it's challenges. I'm still stuck on the second Demon Boss in the first world. But I enjoy the challenge.
You're able to play it online, the whole game is based around an online cooperative mode type of game play. You see other players every now and then as a white phantom figure. You can also active "blood stains", another characters death spot, and watch their last moments, as a red outlined phantom, before dying. There are also messages that other players can leave in the world to help you out and warn you of upcoming dangers or treasures, secret passages.
You can also put down your Soul Tag and be summoned to another person's world as a Blue Phantom. There you can play with that person and one other Phantom (if they summon a second) and give them a hand in the level if they're having issues. This usually happens coming up to a boss.
The game has a lot of mechanics, I find, and it can get a little annoying with how often you can die, but I've been enjoying it.