If you are looking for a game that will challenge you like during the days of NES/SNES, look no further.
You start by customizing your character's appearance and choosing your class - the beauty being that each class can prevail when you learn their strength/weakness. After being handed the basics in a brief tutorial, you are thrown against a massive demon named Vanguard. At first glance, you think to yourself "there's no way" as he can put you in your grave in 1 hit. However, close observation, planning, learning the combat, and a few trial and error runs will reward you with defeating this bastard early on, rewarding you with a little treat that most people never see and a nice bonus to your character early on.
Either way, you end up dead after the tutorial and revive as a soul in the Nexus, your sanctum - where you increase your stats, learn spells, and repair/upgrade armor using souls from the demons you kill. Here's the catch, if you die once, you drop your souls and have the opportunity to get them back. If you die again before making it to your corpse, you lose everything. It is a relentless system, but it makes it that much more rewarding when you can avoid death and defeat the threats that you are posed with.
The story unfolds after each level's major demon is destroyed, but attaining this is no easy task. It takes patience, good hand/eye coordination, and careful planning to kill even the weakest of enemies - as even they can kill you in a few hits. Traps are around every corner, making it even more challenging. The enemy AI is quite good - they'll team up on you and plan their attacks according to your movement.
Each boss is unique, utilizing specific patterns of attack which you must read carefully if you want any chance of victory. Characters you meet throughout the game will give you choices (saving vs. allowing them to die for example) which guide both the story, the items you receive, and the way some boss fights pan out.
There is a PvP element to the game. Once your character dies and becomes a soul, you have 3 choices to revert back to your normal form. Choice 1 is using an item (limited number found throughout the game). Choice 2 is downing a major boss. Choice 3 is invading another living player's world and defeating them in PvP as they traverse through the same level as you. This adds yet another hurtle in the game, and keeps you on your toes both while you are alive and while you hunt the living to get your own body back. Later in the game, you can choose to duel other players - the loser drops one level, and the winner gains the amount of souls needed to attain that level. It adds some competition without being too vicious if you lose.
All in all, this game is not for the faint of heart. If you can withstand dying many times, using your brain every minute you play, and are up for a huge challenge, you will be rewarded for your efforts every small step of the way. If you are looking for a game that just goes through the motions and forgives laziness, looks elsewhere.