Quite frankly, Demon's Souls is not a game for everyone. The mechanics aren't the most intuitive, and the game clearly expects you to put a lot of effort into learning how everything works. The difficulty level is punishing at times, and death is almost inevitable. Players who expect to breeze through stages will find themselves quickly dying as they haplessly wander into an enemy ambush.
If you're willing to take the time to learn Demon's Souls, it can become an exceptionally fulfilling experience. Making your way through the difficult dungeons is often exciting and fun, and it's difficult to match the sense of satisfaction you get from crushing a boss or escaping a black phantom. The online capabilities really add a lot to the game; being able to call in other phantoms to help is a great idea, and the added tension that comes from fearing an invasion keeps the levels from becoming dull, even if you've already played through them multiple times.
For those willing to put in the effort, Demon's Souls is perhaps the most rewarding RPG available on the PS3 and easily a must-have for any PS3 owner who doesn't mind a bit of difficulty and death.