What is "depth" in combat, and how does it relate to combos? Part 1 of 2

There's this idea that a combat system isn't "deep" unless it involves artificial input complexity. I see this a lot in reading up on beat-em-ups - the first acknowledgement is usually that "this game isn't particularly deep, as there are only two buttons: one for attack and one for jump, and only one combo string - attack, attack, attack". It's rarely (and by rarely I mean I've never seen it) acknowledged that this is a gigantic logical leap unless depth is explicitly defined as "the presence of multitudinous input facilities", which just doesn't sit right with me. That logic would lead to the conclusion that Bit.Trip Runner has deeper gameplay than Super Mario Bros. because it uses more buttons. I get where people are going with the "lots of stuff to do = more choices = more variations = depth" logic, but I think it's a little too quickly become second nature. What about when all of those buttons do the same thing? What about when the player can't tell the difference between the combos? What about when variations are provided through means other than direct input? For example, strategic variations? I'm pretty sure chess can be played with one button. What is the relationship between input complexity in combat and gameplay depth?

Sources tell me this is what chess will look like in the future.

First of all, what precisely do we mean by "depth"? Depth as I understand it is a measurement of the number of means available to the player to create a unique challenge from a presented scenario. So a game that only provides a single means to overcome each situation - say, Pitfall, in which there is an exact jump you have to make to cross each pit - ranks at the minimum possible gameplay depth, as there is only one unique challenge present: hit "jump" at the right moment. A game that provides near infinite means to overcome approach each situation - say, Ogre Battle 64, in which your battalion is made up of dozens of uniquely evolving members whose growth is affected by every decision you make, thus influencing the available factors to fight the next battle - has an incredible amount of depth. The challenge of a mission is dependent on what units you have available to you, and those units will be unique on every playthrough.

Much of the depth of a game may be non-obvious - "deep" games are often associated with "hard to learn", as the gameplay variations usually must be explored and uncovered by a careful player. For instance, a new player approaching Alien Soldier will get some instantaneous depth from the weapon choice. When they reach that first purple centipede boss, they may be firing away with Buster, Sword, or one of the other six Forces, and this alone creates a wealth of strategic choices (without even getting into ammo management and whatnot). The battle will play slightly differently depending on the weapon choice (using Ranger the player can stay on the run but the fight will take a long time, using Lancer they need to wait for openings to peg just a few powerful shots), but is still made to be won with any of them. A more skilled player will learn an even more direct approach to the boss - play the preceding level carefully enough to maintain full health (or use counters on the boss's projectiles to grab life-ups) and then nail a single Phoenix Dash while the boss is relatively still - this is a one-hit kill. This strategy is tougher to pull off and quicker if done correctly, but it doesn't supplant the gun-based strategy of a novice. It's a totally unique challenge, no longer about dodging and aiming but instead about conserving health and then aligning a single dash attack. This is how learning can translate into depth.

How do we apply the concept of depth to melee action combat? Every game develops its own notion of depth through the means it presents the player choices and situations. If the primary goal of the game boils down on a moment-to-moment basis as landing hits without taking too many consecutive hits in return, the choices will probably revolve around "ways to safely land hits". Take Streets of Rage for instance: the player can safely land a hit by punching (only when the enemy is not attacking) or by grabbing (from the side) or by jump-kicking (which has long range but is easy to miss). There is no clear "right" way to land a hit in any situation, so the player can arbitrarily select from these choices - all of them will always work if timed correctly.

So on the surface they seem superficial - isn't the challenge always just to land the next hit? The difference - and thus the guidance for the decision - is what happens after each attack, the way the attack translates the current situation into the next. After a punch, the player is in exactly the same situation as before, but can quickly throw another punch or switch to another attack. A jump kick will instantly knock down its target but leave the player vulnerable for a lengthy period of time. A grab presents A SECOND choice: the player can continue to pummel the grabbed enemy for heavy damage while remaining totally vulnerable or throw them over the shoulder to clear out neighboring foes and create an open space in the direction of the throw. The choice of attack is not arbitrary - it can create a widely different subsequent combat scenario. Using throws spaces enemies out, while using jump attacks keeps them on the ground. Concentrating on punches can help kill off targeted foes fastest. Fighting spaced enemies requires different strategy than fighting a close crowd and killing off certain individuals first can change the way the crowd functions. Thus, the player's attack choices have dynamic enough effects to be directly responsible for the flow of battle, which is that key aspect of the "depth" definition: creating unique challenges.

Perhaps in that case we should expect depth in a combat action game to be associated with a one-to-one relationship between inputs and outputs - that is to say, the game plays differently depending on how the player plays, where "plays differently" means "presents a unique set of challenges". If each choice leads to a new challenge, a multitude of choices would provide a wealth of challenges, and hence, depth of gameplay. It's clear from the definition and the above examples that there's more to depth than just lots of buttons and combos, but we can also see how lots of buttons and combos could easily provide lots of options and hence depth. Let's take a closer look at one particular action game (a beat-em-up, naturally) to see how complex input choices starring combos don't necessarily translate to unique challenges (and hence depth). That game'll be Sengoku 3 - tomorrow.