I love this game so much. Really, it's my favorite game of all time. It's amazing on so many levels.
The mechanics aren't explained overtly but are revealed by reading item description and other player's hints, talking to npc's, and through player experimentation (with little chance of screwing yourself over). An air of mystery in the mechanics, the story, the world, and the secrets is one of the game's greatest strengths.
The art is incredible. The artist that made it never calls attention to himself. You never think, "oh this guy was really trying to be edgy" (dead space). It just is what it is... and that's how the whole game feels to me. It feels crafted as anything this meticulously made does, but it rarely calls attention to that fact. Like how Nintendo games used to feel like they were magically created instead of made by programmers and designers.
(warning, minor spoilers)
Seamlessly travelling throughout the world is not only a tremendous feat but adds to the game in big ways. When you go deep underground (burg > depths > blight town > demon ruins for example) you really feel underground and isolated. And when you start getting a hang on the game's challenge you still feel vulnerable. That balance is so hard for other games to find but it's a must in keeping you immersed in the game. And the world! It's so mysterious. If I was a kid again I'd be doodling dark souls monsters and levels all day at school.
This is a gamer's game in all ways. It's truly rewarding for people that aren't new to the medium. It makes few compromises in its hardcore vision but it's almost always fair.
The only thing that has me scratching my head is why more people don't feel this way. I know both souls games have large followings, but as brilliant as this game is, it should be larger.
Anyway, I still haven't finished the game once. I believe I'm about 80% of the way, though, and look forward to new game plus where I can start focusing on discovering all of the game's secrets... and PvP.