Some games use the apocalypse as the Big Evil That Must Be Averted. Some games use the apocalypse as backstory to help establish a setting. Darksiders uses the apocalypse as its tutorial level.
Of course, seeing as how you're War, one of the Four Horsemen of the Apocalypse whose job it is to preserve the balance between Heaven, Hell, and Man before finally ushering in the End of Days, it does make sense that you'd feel right at home in the Final Days. Unfortunately for War, it turns out that he wasn't supposed to be ringing in the Endwar after all, and so he gets chained as a prisoner to face the wrath of his masters in the Council, and unleashed on the human-less Earth 100 years after the demons took over in order to right the Balance and get his revenge.
Unfortunately for the player, the opening tutorial does a very poor job at convincing people to play Darksiders. It's empty, it's shallow, it consists mainly of "go to this area, kill these guys, etc," and it makes the game seem like a rote, run-of-the-mill hack-and-slash like God of War, only without the super-awesome combat. It isn't until an hour or so in, when you reach the game's first true dungeon, when you realize that Darksiders isn't God of War or Dante's Inferno or Bayonetta after all: It's The Legend of Zelda.
On some level, action games have always had an element of exploration and puzzle-solving to them, but while God of War et al lean very heavily towards the "combat" end of the "combat-and-puzzles" spectrum, Darksiders gleefully jumps into the "puzzles" part. War's massive sword and thick armor might suit him well in combat, but he'll be running, climbing, pulling levers and pushing blocks as he explores the demon-infested ruins to defeat the lair's Chosen.
Some puzzles are tougher than others - some had me scratching my head for a while, others I figured out in a few minutes at most - but if you're going in expecting to beat the game just by rushing through guns blazing, you'll be in for an unpleasant surprise. It's telling that while there is a time-slow mechanic in the game, it isn't reduced to the tired old "bullet time" combat feature as in most games it appears in; you use your time-shifting to solve puzzles.
Of course, while the "go to place, get item (or power), use item (or power) to go places you couldn't go before, explore to find hidden goodies" formula works well, this isn't to say that you'll never be fighting. Darksiders' combat works very well, with War possessing a nice variety of primary weapons and little gadgets, from his gun to a throwable shuriken to a grappling hook (and even a Portal Gun, surprisingly). You can purchase new abilities and new ranks thereof from the main merchant, the combos flow together easily and intuitive, and fights are cool-looking, exciting, and brutal - particularly when you execute the simple-to-pull-off finishers.