A sign of a good game is often recognized in a players emotional attachment. Many of the "Top X" lists of games all have those highly emotional intense moments that stick out as the most memorable. Look at a random "best of" or similar list and see how many you know and what comes to mind first. Regardless of your personal view on a given list or game within it certain games pop up on a regular basis. FF7 for example, and a great many people remember when Aeris dies as a key moment in the game and one of the first things they think of when it comes up. That's because the game up until that point had the player building a relationship with the character so her death becomes significant and that emotional bond then gets played on to make the player personally fueled to get revenge or justice what have you.
For me MGS3 was one of the only games that ever brought me to tears, one of the few things in my adult life for that matter, and it can still do it years later. Today I'm looking at how developers exploit human emotion. I'll use MGS3 as my analysis point so if you haven't played it, I suggest you do so then come back and read this, as it will likely contain spoilers.
Before I get in to it I'll take a moment to acknowledge Quantic Dream. If you're unfamiliar with their work I suggest playing heavy rain or viewing their Kara demo on youtube. Their emphasis on emotion in games is unparalleled. Whether this is a good or bad thing is irrelevant compared to the achievements in and of themselves. I look forward to seeing what they do in the future, including two souls and beyond.
Now that you've had a chance to get away and back it's on to the lesson. There's a multitude of ways developers find ways to connect the players with their characters. They often try to get you to empathize with your character laying a foundation to build on so that you think of the character as an extension of yourself. The Mass Effect games do it by allowing you to build the character, the choices are actually yours. While MGS does it through dialog and ICO does it through raw player interaction, and Dante's Inferno does it on story. Granted Dante's Inferno was based on an existing story, but it's for the same reason that the original was such a great story. For those of you unfamiliar Inferno was the first of a 3 part story. Dante takes a journey through hell on a mission to save the soul of his wife which was condemned for his sins. That kind of emotional tie leads you to empathize with Dante and hope he succeeds, and in the game the only way he can do that is through the player. In MGS you can rush right through and get the game done but that's not really the full experience. If you really take your time you find yourself relying on a team who believes in your abilities to save the world from nuclear war during cold war as an American special agent infiltrating Russia. You learn to rely on them for help and advice because they know things you don't, about the enemies you'll be facing, the weapons they'll be using, the environment, how to survive in the wild. In the process you learn a lot about them on a personal level, what they like and dislike, their personalities. You come to understand that they're not just hoping or relying on you, they honestly care that you survive they have real feelings for you.
These emotional bonds develop not only between the characters but with the player as the player is playing both the support and the main character allowing them to empathize in different ways. Which makes even early on the betrayal of a colleague a strike to the heart. You realize there's a complex emotional bond and can't understand why this is happening, making you want answers more than anything. But you have a responsibility to fulfill your duty, and you understand that the betrayal can't go unpunished. Your journey leads down a path of personal development, strength and determination to succeed. With your team firmly behind you every step of the way as you face tougher opponents standing in your way not only to your mission but your personal goals. The little support you get in person instead of over the radio is critical and right when you need it the most. This relief in an extremely stressful situation leads you to almost completely trusting in this additional support. Just when you think it's all over though it's violently ripped away from you as you realize you're all alone in the world under the burden of a secret no one can ever know. It turns out the greatest betrayal against you is the one you didn't see coming, your own. When it's all said and done amidst all the lies and half truths you learn that not only were you not truly betrayed to begin with, but you were in fact betrayed by the ones you've learned to love and the ones you blindly followed but in the end you were tricked into betraying yourself. The fact you're mourning the loss of someone you care about so much is compounded multiple times by the fact that it's your fault, that it was under false pretense, that they knew it was coming and went along with it anyway, and more. You saved the world at the cost of your soul and humanity, how could you ever recover. This highly complex story and set of emotions under the right circumstance can have an extreme effect on the player.
There's a wide variety of emotions though and you can't just explore one. Dead Space for example plays on fear. The developers immediately set off to put the player in a state of fear and keep them there, in the dark, alone, and with little to no resources. It's a struggle for survival in an inhospitable environment against an unknown enemy. One of the main ways they keep the player on edge is with sound. The music of the game is designed to have the player paranoid not only about every corner but out of anything and everything as an enemy could come from anywhere at any time. Regardless of the shadows you see moving in the background or not all it takes is that one note from a violin I believe it is and you're on edge, sometimes for no reason. As you examine the ship and relive the last moments of the people aboard you only sink deeper into this feeling that there's no way out, that you're doomed, how could an entire ship succumb to this and more importantly how could you hope to survive against such a force. You know your death will be violent and your only hope is to press on, and that's all you have is the slight glimmer of hope that just maybe you might survive. That hope in itself also leads to a slight hope that if you could survive maybe your wife could to, maybe she's still hiding somewhere waiting for you.
Look at all your favorite games and see if you can identify the primary emotion of the game. Portal is likely hatred, directed at Glados for making you kill the companion cube and for trying to kill you. Silent Hill 2 is love for a child and doing whatever it takes to save them. Mass Effect is a case of extraordinary circumstance and the ability for the player to imprint themselves on the character. Still it works from a complex emotion in which there's a bit of hatred and desire for revenge and yet it's not the focus. It tries hard to fall into a vague or gray (grey? what's the actual difference?) area and yet I'd have to say it's primary focus is trust. Regardless of your choices you're constantly building trust between you and your crew. That's fairly true of most bioware games which seem to emphasize the importance of the grey area in choice.
This is already a very winded post, so I'll cut it short. Hopefully you managed to gleam that games and emotion go hand in hand and that it can make or break a game.