Open stats system
"Dark Souls doesn't force the player to play the game in any particular way. Want to play a heavily armored knight, a light-on-her-feet warrior, a mage, a priest, or all of the above? Sure thing. The game lets you use the style of hero that you feel most comfortable with." (Boyd, 2012)
If Dark Souls were a university, the player's major would be undeclared. Sure you pick a few stats (or courses) at the beginning, but those choices act as trial periods. Over time, as you try different play styles, you are able to commit to the ones you like best.
Dark Souls relies heavily on the mechanic of souls. You gain souls by killing enemies, with larger payouts for bigger baddies. You can spend them in a variety of ways - to purchase new items and gear, to upgrade existing gear, or to level up your character. Purchasing a level grants one stat point that you can put into any of the base stats. Rolling a Priest? Upgrade your faith. Playing a Tank? You’ll want some strength. Want to play a Paladin? Then go half and half. Any character can upgrade any stat without limitation. But stats don’t merely improve your character’s attributes, they also increase the scale with which weapons deal damage.
The weapon system
Dark Souls' weapon system is unique and peculiar. For starters, each class of weapon comes with different attack patterns, animations, and attack speeds. Each weapon class feels different; each has a different weight. Sword swings may bounce off the narrow sewer walls, but a thrusting weapon with minimal horizontal movement (a spear) is perfect for the occasion. Weapon damage scales with stat points. In each weapon class, you'll usually find at least one weapon for each stat. And to add fuel to the complexity fire, you can upgrade weapons to scale with a different stat entirely. Dark Souls is able to put all of this together to form one of the deepest and most engaging sets of fighting mechanics ever devised.
The bonfire mechanic
But what happens when you fail and inevitably die? This is a hard game, after all. There are bonfires scattered throughout the different areas. Bonfires are safe-havens. They serve as respawn points, level up vendors, and reset buttons. That last item might sound a bit odd, but bear with me. When you rest, every enemy in the game (except bosses) resets health, location, and aggro status. This affords ample opportunity to learn how the surrounding area works. Monsters respawn with perfect regularity as you die and reset bonfires. To get far in Dark Souls, you must understand your enemies. This is daunting at first because every enemy type (and there are hundreds) have different attack patterns, different animations, and different AI. There is no "One Size Fits All" solution to this game. An attack style might absolutely decimate rabid dogs but be worthless against crystalline giants. Each area has a spattering of different enemies which keeps the game feeling alive and compelling.