"I have simple tastes. I am always satisfied with the best."Just as a character arc is the development of a character's choices over the course of a story, the depth of a game's play depends on the development of choices that the player makes.Oscar Wilde
The problem with giving players choice is that there is simply too much fun to be had by killing the player. Remember Choose Your Own Adventure? Those books were definitely written simply for the joy of writing loads of unhappy (and violent!) endings, because it sure as hell wasn't very much fun going back to the start and trying again.
If one choice is simply better than any other, then there is no decision to be made at all. However, the opposite is just as ineffective: If no choice yields a reward greater than any other, then there is still no real decision to be made.
Giving the player one right answer either forces him to play along in the developer-created charade or makes him feel like a fool for not knowing what the right answer is, while not allowing the player the chance to make any wrong choices gives him a pampered and boring experience. These are both effective at insulting a player's intelligence.
The overall objective in allowing the player meaningful choices is to give him multiple exclusive choices that can all be considered appropriate (that is, the game offers a satisfactory reward).
Enough academia. Let's talk about punching people.
The best part of beat-'em-up games is that there are always a couple super awesome bad-ass moves the player character can use to break fools.
The problem with beat-'em-up games is that there always a couple super awesome bad-ass moves that player will choose to do instead of the vast majority of the others.
A major byproduct of the move from 2d to 3d graphics is that animation is far more easily tasked to a larger group, and more effectively and efficiently QA'd. This is why the movelists of 3d fighting games absolutely dwarf the movelists of their 2d brethren. In theory, this should account for a quantum leap in the game play of this type of game by expanding the number of choices to the player.
At the end of the day, it does very little. It doesn't matter how many different punches and kicks a player is able to do; once he learns how, he will only ever use the most effective ones. In fact, a major hump in the learning curve of any modern fighting or beat-'em-up game is understanding which moves are just bad, and how to avoid accidentally doing them.
Running around a game environment performing the same overpowered move to everyone to achieve the mega-objective (i.e. kill everyone) is not nearly as fun as making split decision choices to in order to achieve some meta-objective (e.g. maim chosen enemies in specific ways). The latter also gets a bonus because the meta-objective is one that the player will create for himself.
So how are modern beat-'em-ups encouraging players to experience all the cool moves that the developers slaved away at implementing? Let's take a look!
Devil May Cry
DMC games have also included a Style Meter that instantly presents a meta-game; while the player's health and the enemies' deaths measure how well the player is doing, the Style Meter measures how awesome the player is doing. Simply killing everyone on screen (mega-objective) is not enough-- the player is enticed to try to get a "SSStylish!" ranking for a fight (meta-objective).
Not only does the Style meter offer big bonuses to changing weapons or taunting enemies mid-combo, it creates a diminishing-returns system: each time a certain move is performed, it offers less boost to the Style meter every time afterwards. After the third or fourth time, doing that same attack will begin to hurt the Style meter, actually punishing the player for relying on the same crutch move.
The Stylish rating achieved when an enemy is killed determines how much money the player gets from the kill-- and the money is used on buying more attacks, which will only allow the player to get higher ratings the next time around.
Dead enemies in NG games release their souls to the player in three flavors: Yellow (money) Blue (health) and Red (magic). While they are in itself a reward to the player, they present an important choice to the player: the player can choose to either let his character absorb the essences to reap the immediate benefits, or he can allow his weapon to absorb the essence in order to unleash an Ultimate Technique supercombo. Both choices are extremely rewarding.
Also, enemies in NG can survive losing one extremity (in some cases, head included). This, understandably, will change the abilities of that enemy character, which opens up huge tactical options. It also gives some individual character to the many different combos-- XXY with the Dragon Sword will cut off an enemy's left arm, while Forward+Y with the Falcon's Talons will usually clip a leg. Designing enemies so that the player wants to remove the arms from ranged attackers, the legs from nimble pursuers, and heads of zombies, offers a great reward to the player for exploring the huge move set.
God of War
God of War is famous for its finishing moves, and rightly so; every enemy in the game has a brutal character-specific for its demise at the player character's hands. This creates considerable variety in the player character's actions (as he'll perform different moves on different enemies) and also creates a very accessible "small-in-big-out" design that allows a wide audience to experience even the coolest moves the game has to offer.
The problem is that once the player has seen all there is to see, he grows bored of shoving burning blades down the throats of minotaurs from the same camera angle every time.
Though I suppose once you are tired of shoving burning blades down the throats of minotaurs, you are tired of life.