The two games in the 'Souls' series, are a blend of precision action, and RPG.
You begin Demon's Souls by picking from a pool of various classes(Knight, Wanderer, Royal, Magician, Hunter, Thief, etc) going through an incredibly easy tutorial, slaying enemies effortlessly. The tutorial teaches you the ropes of how to play, how to time attacks against enemies, and block everything with your shield. At the end of the section, the game pits you up against a boss, that kills you in one hit. Now, it's entirely possible to beat the boss, as it's attacks are slow, and it gives you lots of openings, but if you slip up even slightly, you're a dead man.
This is the best way to introduce you to the way the game works. Demon's Souls is a brutal, no nonsense game. Timing and positioning is everything in combat. Along with your health and mana meters, you have a stamina meter, that recharges quickly, but is consumed every time you use an attack, or block an attack with your shield. A lot of the game you'll be micromanaging your stamina, trying to make sure you have enough to keep from being staggered, as well as fight back.
Almost all the enemies in the game can kill you incredibly quickly if you don't know what you're doing, so you always have to be on your toes to keep from living a short life. Speaking of life, you will spend a fair chunk of this game "dead", or more specifically, in "Soul" form. When you die to the first boss(which 99% of people do), you are revived in the "Nexus", a ephemeral room that traps you from passing on into the afterlife. The Nexus is your primary hub, where you can travel to other areas, get items from the shopkeeper in exchange for souls, and level up using, once again, souls. Souls are the "experience points" of this game, and they are key to your survival. As you defeat enemies and bosses, you'll rack up these souls, however, if you die in a stage, you lose ALL of your souls that you have not spent yet. Yep. If you manage to return to where you died without dying again, you can reclaim your souls, but if you're unlucky enough to die again, they disappear forever. This is accented by the fact that the game is constantly autosaving after every instance of pretty much anything, meaning there's no reloading your save if you screw up. You accidentally attacked a shopkeeper and they turned against you? Well, that's saved and you can never buy from them again, unless you start a new save.
This game is great at creating a sense of realism with your actions, as there's no going back from anything you do, forcing you to choose everything carefully, and really make sure to not screw yourself.
I'm currently not even half way through Demon's Souls, and when I'm done with it, I'm pretty eager to start Dark Souls. I'm loving the challenge and intensity of the game, and if you like games that force you to persevere through constant crushing defeat, give one of them a try.
Dark Souls just came out on Steam recently for $40(it's also $20 for PS3 on Newegg with a promotion code today), and you can pick up a cheap copy of Demon's Souls for around $15.