Challenge is necessary to bringing out and creating the depth in a game. Without a game actively resisting you, it is a lifeless ordeal.
In a recent (editor’s note: HAHAHAHA) Overgrowth update video, the programmer revised the AI algorithms in ways that generally had the enemies become more difficult to combat. At the end of the update video he made a statement on the matter, “The purpose of all these AI improvements is not to make the enemies more difficult, but to make them more engaging so that the most interesting way to play is also the most effective.”
The big goal with difficulty isn’t to make things hard for the purpose of being hard. It’s to generate interesting scenarios and strategies and to make the game “easier” for people who play it better instead of cheese it out by abusing one tactic. It’s to reward people who figure it out and beat down on people until they figure it out, because figuring things out is fun. It’s about creating a feeling of real success and achievement, not just a validation of the self. Difficulty is about making people work together to learn and succeed. Difficulty is about rewarding dedication and effort.
But again, difficulty is not everything. A game being more difficult by default doesn’t make it better, it just makes it harder. Sometimes a linear increase of enemy health and damage can seriously up the ante, but these shouldn’t be the only methods considered for increasing difficulty. There are tons of interesting ways to introducing difficulty into a game, such as creative forms of punishment for failure (remember how demon’s souls would take away half your health for dying and decrease the world tendency, making the game harder? (also increasing drop rates)), special enemy behaviors (like the aggro range of some enemies affecting larger groups of enemies), lethal health systems (like Doom 3’s hardest difficulty which only lets you have 25 health to start and any health you accumulate over 25 slowly drops until you only have 25 left), or creative difficulty scaling systems (like God Hand’s level up meter that increased as you did damage to enemies and for doing tricky sidestep dodges and decreasing as you took damage and died, increasing the amount of bonus gold you got at the end of the stage, but also increasing enemy damage and making the AI more clever and aggressive).
In my Dishonored review I remarked on the myriad ways which the game lacked in both the stealth and lethal methods of play. My fixes for all of them were things that incidentally increased the difficulty. Dishonored’s central problem was that the enemies you faced had no real method of dealing with all the massively lethal powers you had, from giant blasts of wind, razor traps, swarms of rats, or even your simple gunfire or any capacity for intelligently engaging a hidden player. It was a game that tried to prize intelligence and clever solutions to problems, yet it made for a game that could be broken without effort with any single tool in your arsenal.
Deep games can of course exist without difficulty, however they are limited in how deep they can truly be. Dishonored had all the tools to be a deep game, but without more challenging level design and AI, the strategy involved in playing the game will always be simple.
A lot of people fault games for having harder difficulty modes that are nothing but enemies that have more health and do more damage. Frankly, I think this is a totally valid way to increase difficulty. The common argument is that this does not make the game harder, only that it takes longer to kill enemies. I don’t think this is true. When enemies do less damage, you are given more free reign to tank hits and this can lead to playing an encounter very differently from a situation in which you are dealing with a highly lethal enemy. When an enemy has less or more health it encourages the use of different weapons as well so that they can be dispatched efficiently, such as taking out a rocket launcher for the large enemies that do more damage than the normal ones. When an enemy has low health, it opens up the tactic of launching an attack that would normally trade hits, but kills them before you take damage. That said, merely increasing damage and health is a viable way for making a game harder, and it can alter the way one approaches the game strategically, however it is still a lazy way to increase difficulty relative to more tangible changes like additional enemies or limited resources or otherwise.