So when it came to making Uncharted 2: Among Thieves (U2) we wanted to evolve the combat and help bring it into its own. We knew we had a solid foundation to work from, so it was a matter of taking the lessons we learned and playing to the strengths of our core mechanics better. Here's a high-level synopsis of the key goals we wanted to tackle.
Many of the goals we set for ourselves helped to reinforce this one idea, to give more tactical choice to the player during combat. In U1 the encounters that we enjoyed the most were in places where the player had more choice in how they wanted to tackle the encounter. We wanted to find ways to emphasize that sense of tactical freedom even more.
A key goal in support of Tactical Thinking was to exploit more gunplay while the player is traversing around the environment (which we call Traversal Gunplay). This includes shooting while hanging, while walking on a balance beam, or while jumping.
We did touch on this in U1, but there were limited times when it was really usable, not to mention Drake's move set didn't support shooting from all of his modes of travel. Also, our AI did not have the ability to traverse around the environment to follow the player.
Sorting these issues out became our first goals for U2. For the player we added the ability to shoot from just about any of Drake's traversal mechanics, allowing the player to engage in combat regardless of position or action.
For the AI we created special objects we could place in the world that would allow an AI to play an animation to be able to get from one place to another. We called these Traversal Action Packs (TAPs for short). Things like climbing or jumping down a vertical surface, using a ladder, jumping across a gap, using a balance beam, etc.
Using our enhanced Traversal Gunplay mechanics we were able to expand the play-space not just horizontally, but also vertically. Allowing the player to find places they can climb to gain an advantage proved to be a lot of fun and very engaging. Combat no longer had to be point and shoot, but also could become a sort of puzzle where the observant player could think of creative ways to use the environment to their advantage.
Another tactical element we didn't get the chance to explore in U1 was stealth gameplay. In U1 the player was almost always on the offensive with no real way to sneak around. For U2 we wanted to open up this tactical option to the player.
The trick was making sure we kept the pace up as traditional stealth gameplay tends to mean creeping along really slowly and looking at stealth meters. This wasn't the tempo that we were going for with Uncharted. "Action Stealth" was our motto, meaning our stealth had to be fast-paced and simple. We purposely simplified the design to be as player favoring as possible to prevent players from getting frustrated with stealth and abandoning it.
Our key reasons for including stealth gameplay were to utilize the tone and mood of stealth to support our narrative, and to give the player more tactical options on how they wanted to start a combat encounter. This would give the player the ability to get a leg up on a combat encounter by quietly eliminating a few enemies, and then getting into a good position to start the combat (usually with a bang).
In U1, once combat was started the AI would always know where their target was (usually the player). This didn't result in a lot of opportunities for tactical thinking, so for U2 we wanted to make the AI less perfect in this regard. They could now track you based on information gathered from their senses and their fellow AI instead of outright omniscience.
Sensory input includes their vision and hearing (weapon and explosion sound locations only) in addition to the location data they get from their fellow AI that have spotted their target. If they lose sight of their target, after a while they go into a hunting mode starting with the target's last known position.
From there they'll begin searching other positions radiating outward. They also have to acquire their targets in order to hone in on them -- meaning if they're coming into an area blind but they know someone's there (such as after hearing an explosion), they'll aim at the location of the disturbance rather than right at the source that made it.
This allows the player a chance to be crafty and outsmart the AI. For example, if the player's been spotted on one end of a long piece of low cover, he can move in cover to the opposite end and see the AI is still targeting where the player was originally. These might seem like minor points, but it's the little details like this that help to bring a bit more human quality when engaging them.
To give our combat more depth, as well as to keep it from getting stale over the course of the game, we wanted to introduce a greater variety of AI for U2. We touched on this in U1 with the shotgun and grenade launcher class of pirates, but for U2 we wanted to expand it further. In addition to shotgun, rocket launcher, and sniper classes, we added a fully armored class, a heavy class that wields a mini gun, riot shield class, and we separated our basic grunt into light and medium classes (the light and dark uniformed soldiers).
By mixing and matching various combinations of these classes and weapons, it allowed us to create combat encounters that would force the player to make on-the-fly tactical decisions. This also gave us the means to create a stronger overall difficulty ramp across the entire game. By training and introducing tougher and tougher enemies and then tougher combinations of enemies based on the encounter space, we could keep the combat exciting, giving the player something different to experience with each space.