Dark Souls is fun and annoying all in one.
The game itself is surprisingly linear, unless you're very good at the game. Their is only one distinct path to travel up until a certain point. That's not to say that you can't stray off into different areas, or paths, but you just shouldn't. The enemies in this area, far out-weigh your weapons and stats.
That being said, that doesn't make the game boring or uninteresting, because you'll hardly realize it until you can take a step back from dying to the enemies strategically located in the some very inconvenient locations on the map.
The game is massive. Not just in terms of map size, but the amount of weapons, armor, and secret treasures are around every corner make this game very big. There are plenty of areas to satisfy.
The bosses in this game are great. I enjoyed just about every fight. Some were easy for me, others I had to use a specific strategy to defeat.
The Multiplayer. Where do I begin? It barely works? Nah, that's not good enough.
Player vs. Player on this game is very laggy. I don't think I've invaded or been invaded by anybody that I haven't seen skipping around my screen. Not to mention, invasions happen at random. It's fun sometimes, but it's mostly annoying. Luckily, they've made a couple of ways to stop invasions.
Playing cooperatively is a blast. You're always rewarded for helping. It's also worth mentioning that its a lot less laggy than PvP.
The thing that drives me crazy about Dark Souls is the Button-Delay and Invasions. The buttons will fail to process commands to your character often and sometimes they'll process 1-2 seconds too late. You'll find yourself attacking while you're blocking yelling "WTF" while you take a massive hit by a boss to end your fun. The Invasions are mostly annoying, because if you're trying to play cooperatively in certain areas of the game, it's just close to impossible.
Overall, Dark Souls is worth getting. It's a little less of a game than Demon's Souls in my opinion. It has nothing to do with nostalgia or Demon's Souls being the first to introduce us to this style of game. So, if you're hoping for it to be as good or better than Demon's Souls, that's for you to determine. Either way, it's a solid game.