Well, I have really been enjoying the heck out of this game. The world, though, is sometimes like hell. It's very scary, and it's very dangerous. I have a feeling I am going to be playing this for a while longer until I've experienced the entire game. Highly recommended.
Try out the Temple Knight class for Heavy Armor. Although you'll want to switch to a different weapon than the Halberd, such as a Long Sword. Whatever class you pick, if it's melee, I would train a bunch of Endurance.
So yeah, the game is very tough. The first level is tough. If you can get through it, and at least the first level of each other world though, you should be able to beat the entire game if you stick with it, and have patience. It's a lot of fun. Some frustration, yes, but very rewarding. Ultimately though, I would say the difficulty is a bit too high. I think this about other games too though, so maybe it is just me.
There is a New Game Plus (NG+) function, which allows you to play the game again. The catch is that the difficulty is increased by as much as 40%. Yikes! The new game plus was indeed...frighteningly difficult. My character in Demon's Souls needs to have a more focused build.
I started a new game with the Hunter class and I've been enjoying that as well as the online multiplayer experience. It's fun to join someone else's world and fight a boss together in order to resurrect yourself.
There's also a sequel called Dark Souls coming out in October, on both Playstation 3, and Xbox 360. I will get it for my PS3. In fact I already have it preordered.
I hope that they reprint the Demon's Souls Deluxe Edition w/ Artbook & Soundtrack CD, which comes with a strategy guide. They can be found on ebay and Amazon, but they are overpriced. Oh well.
All in all Demon's Souls Greatest Hits is an amazing single player experience rpg with an online mode as well. It may ocassionally be frustrating, but the experience is worth it. It has changed the way I think about action rpgs.