A better version of Demon Souls
Dark Souls is for people who like a real challenge and don't mind being patient in their gaming. The upside to this is that it's very intense - it's like a great thriller film where you don't know what is going to happen next.
The downside is that it can be stressful and frustrating, especially after a hard day at work. Grinding and retrying strats can be rewarding to some, tedious for others.
I would give Dark Souls a 10 if it had an easy mode for players who just want to experience the world and the combat - for both are truly great - but don't have a lot of time to spend gaming b/c of real life stuff. But even as it is it's a great game, probably one of the best on consoles.
If you can spend at more than a couple hours a day playing a video game, this is the one, especially if you like rpg action. This is 10 times better than any of the Diablo games. It eats Diablo for breakfast.
I just wish they'd given us the option of an easier difficulty. I had the same feeling about Demon souls, but I still played it to several hundred levels on my characters.
A note about grinding: usually it's boring in a game. But when the challenge is there and you can mess up, it's actually fun in this game. So if you buy the game, you need to just say to yourself: I'm gonna die. Let's be calm and patient and accept our death and build on that.
Oh, one note: I think the game is easier, if you're having trouble, if you get a magic user. I took a sorcerer, and the first parts weren't too hard. I hear pyromancer is even easier. Ranged attacks are your friend in this game, as they were in Demon Souls.