I just started playing Demon's Souls on the PS3. It's a 3rd person MMO-like RPG action game. Very intense. Very difficult game. No online fee. Atlus games don't see a PC port, so, it's PS3 only.
The Wikipedia site covers most of the basics. The classes are pretty interesting and offer more than a single choice for a new or seasoned player; http://demonssouls.wikidot.com/
There is PvP. And, you can choose a light/dark side which is determined on who you kill. If you invade another player's world and kill them, you move toward dark. If you defend and kill an invading player, you move towards the light. The same applies to NPCs.
The combat takes some getting used to. You will experience hordes of enemies swarming you. Towering bosses. Griefing, etc.
If you have a PS3, the game is $30 and worth experiencing the simple fact that you will get your ass handed to you on a plate with 2 side dishes.