Stealth mechanics have evolved considerably since the days of Metal Gear. Recently, with titles like Assassin's Creed, games that are built for action have been implementing stealth mechanics which has lead to a design change in stealth titles.
For the longest time, I've never been a fan of stealth mechanics in games and to shock everyone, I've yet to play Thief 1 and 2. Recently however, games like Deus Ex: Human Revolution, Assassin's Creed 2 and Batman: Arkham Asylum has made me enjoy the act of sneaking around. As I thought about these titles and why I enjoyed them, I started to think about what goes into making a good stealth game.
Avoiding Detection: The mainstay of stealth games is giving the player ways to avoid being detected, with line of sight as the first mechanic, from there each game usually introduces another mechanic that acts as the unique hook. Both Thief and Splinter Cell had lighting and Metal Gear Solid 3 and 4 had camouflage.
To me, only having a few ways limits the design. The more options open to the player, the better. Batman had the following mechanics:
Hiding in vents or grates
Grappling up to gargoyles
Explosive gel distraction
Assassin's Creed 2 has:
Hiding in objects
Hiding in crowds
Using groups of people as a distraction
Going across rooftops.
Lastly Deus Ex has:
Throwing objects to create distractions
Rooftops or using elevation
Going through vents
Breaking through walls
Looking at games I didn't like, Hitman, besides line of sight had disguises and the last game added in throwing a coin to create a distraction. To me, it never feels realistic to only have a few options of avoiding detection. I can't wait to see a stealth game combine the unique mechanics of multiple stealth games into one experience.
Having an "out": The other problem I have with a lot of stealth games is that stealth is the only option, as being detected spells doom and one of my first painful memories of this kind of stealth design , was with the game Syphon Filter for the PS1. Near the end of the game, the player is required to sneak through a level with no gear, if they are detected the mission ends.
Not having some kind of offensive ability goes back to a thought I had about the horror genre regarding "fight or flight". If the player's only option is to run away or hide, it makes the game more predictable as the player knows that if they get caught, the game is over.
What was amazing to me, from playing Assassin's Creed and Batman, was how powerful the player was and that they could deal with groups of enemies. With that said though, there has to be a limit, or you just have an action game with minor stealth elements.
That was the problem with Assassin's Creed 2, due to sword counter attacks; it really trivialized the need to be stealthy, unless it was for a mission. Batman had two main types of enemies: unarmed and armed, unarmed enemies could be dealt with without having to sneak, but enemies with guns would kill Batman quickly if they catch him. That set up the dynamic of having sections of the game that were pure action, while still providing areas that required stealth.
The issue with AC2 was that they set up the main character to become a complete bad-ass, both as a fighter and sneaking around. Because of that, no enemy could really stand toe-to-toe with the player. Deus Ex HR: had security drones and turrets, which conventional weapons would not work on them. Only EMP grenades, rocket launchers, or hacking them would work. Now, even though these enemies are best handled by stealth, the designers still gave the option of just fighting them.
Failing Stealth: Building on the last point, one mechanic that has annoyed me about stealth games is that being detected instantly destroys being stealthy.
Chances are if you've played a stealth game then you ran into the following situation: The second someone sees you, every guard on the map instantly knows where you are and comes running. While I like having a way to fight back, I still prefer having a way of becoming hidden again. What I liked about Assassin's Creed 2 was that guards had a few seconds questioning the player's appearance before sounding the alarm, allowing the player to either hide or try to take the guard down.
Personally I prefer to see guards becoming alarmed more realistically, such as: if a guard sees you who don’t have a way of alerting their friends, they'll either try to take you out or run to alert everyone. The farther stealth design moves away from guards with mental links to each other the better.
Less Segregation in Design: This section essentially sums up everything mentioned. One of the main ways that has improved stealth design in my opinion is moving away from having "action levels" and "stealth levels" by combining both elements into the same design. In Deus Ex: HR, with exception to one side mission, the game never forces you to be stealthy. Of course, getting into a fire fight outnumbered is going to be tough to get through, but it's not an instant failure.
Having said that, I know that Batman: AA breaks this point, but in a sense it does work. Giving the player a limit to being aggressive can be beneficial, allowing players to decide how long they should remain hidden before the crap hits the fan. Level design moving from pure linear set pieces to a more open setting has also helped here. Before, getting detected meant that you're only option is to go straight through the enemies to your objective, now you can try to run and hide and get around them another way.
Thinking even further back, The Mark of Kri for PS2 while predominately an action title, did combine stealth elements into play. On each level there are alarms set up that will trigger guards to attack the player if they are detected. The player is more than capable of handling themselves in a fight, but it is easy to be overwhelmed. That way, levels are set up for both stealth and fighting without being separated into specific sections.
One of the main areas that game design has evolved is designing games around more than just one main mechanic. Some of the best games developed have combined elements from different genres to create something new. Batman: Arkham Asylum, succeeded because it wasn't just an action game, or just a stealth game, but a Batman game. With successes like the Assassin's Creed series and Deus Ex, it will be interesting to see how they affect future stealth titles, like the upcoming Hitman game.