...one thing this game does so well is unpredictability. You never know just how the next area will challenge you. You might have to do some precision timing and movement to dodge Indiana Jones-y traps (Sen's Fortress), you might have to descend a cliffside in pitch darkness (Tomb of the Giants), or you might be faced with enemies that can only be killed if you're inflicted with a certain status effect (New Londo).
Even
better, is that joining certain covenants will actually change some areas. For instance, being heavily embedded in the Chaos Covenant will open up shortcuts through the underground lava ruins area (not to mention providing you with potential story insight). Running through a certain area of the Darkroot Garden in human form will set you up with the PvP guardians of the forest. Conversely, if you're a
part of the forest covenant yourself, you can be summoned from any area in the game to defend your covenant's turf (winning or losing returns you to precisely where you were initially summoned, so it doesn't erase your progress). Hell, you may even get Disastered by a Gravelord Covenanter, who curses your world to have super-strong enemies to hinder your progress. Invade this player and kill him to return your world to normal difficulty.
Nothing in Dark Souls is ever straightforward, although the mechanics themselves are all pretty basic. What makes it all come together like some of the past masterpieces in gaming is that From Software have taken the game's basic mechanics and done absolutely
everything with them. There is not a point in the game without some wrinkle to keep you on your toes.
I could seriously write about this game forever. Nothing else I've touched this year since I've played it has really impressed me. Everything else seems amateur and a little bit sloppy, even the mighty Skyrim.