Demon's Souls is not just the reason you buy a PS3, its the reason you start gaming.
This game is regarded as difficult. It is challenging but should not stop you from buying it. It has a learning curve and takes patience to get used to but it is very rewarding to kill a boss and cash in those souls you've earned.
The environment is only one of the incredible facets of the game. It reminds me of Ico and Shadow of the Colossus. It is very gloomy for most levels but it is supposed to be, because Boletaria is under siege by demons. You collect their souls and stop the enveloping shroud of fog.
The class selection is somewhat meaningless because there are no restrictions in the game; you can skill up any attribute and so restrictions are based on attribute level.
The sound fits so well with the appearance of the game and although I don't suggest you stop during boss battles to listen to each unique orchestral fight piece, it is more worthy than a mere background song. Thank you for that, Shunsuke Kida.
The gameplay is tactical, meticulous, and engaging. I don't consider myself a fan of RPG's but Demon's Souls is very action oriented. I love how each weapon works differently, how I need different weapons for different enemies, and the unique items i have to use. It is important to mention that there are two forms you take in the game; the living form and soul form. You will figure out the difference when you die.
Each level has its own theme and you will be fighting in castles, ruins, caves, etc. Each level is flawless.
On top of everything, there is online integration. That is, people can leave notes behind warning you whats up a head or alluding you to treasures. Also you can view peoples' "bloodstains" which show how they died. Sometimes semi-transparent players show up fighting near you. You can help and get help from players by leaving marks. Later in the game the pvp aspect begins and you can intrude someones game or vice versa. All in all, the online play is fresh and fun.
Demon's Souls deserves praise on every level and the cons are few and far between
Pros:
Beautifully rendered environment and tone
Fun and addictive gameplay
Soundtrack is perfect
Cons:
Many bosses can be glitch-killed
Many bosses don't require all that great armor you've been slaving away to get. In fact I fought a lot of bosses naked.
There are a few scenarios in the game where I have felt cheated by some trial and error.