For me the Metal Gear series doesn't fit the franchise model of "same game plus one new feature". It feels more like a 20-year-long prototyping exercise in espionage dynamics. Rules are reshuffled from game to game to create different flavors of emergence. Sometimes the same mechanics dropped into new kinds of level architecture creates a different experience. Unlike most videogame sequels the Metal Gear games are actually different games... with only a few notable exceptions.
Metal Gear Solid (PSX 1998) is notable in that shares more with its immediate predecessor than any other game in the series. MG2's additions of crawling, the radar, and enemy alert phases remained unchanged in MGS. Even the wall-tap, which MGS added as a way to distract enemies, was functionally the same thing as the wall-punch from MG2. One thing it did add was camera manipulation. Being the first Metal Gear game in 3D, Solid essentially took MG2's design and dropped it unchanged into a 3D space. Hiding under things now forced the player into a low angle view. Pressing against a wall caused the camera to swing down into a landscape view, allowing players to see down long hallways. And at any time the player could enter "first-person view mode" which allowed them to look at the surrounding environment through Snake's eyes, although in this mode they could not punch, shoot, or otherwise interact. Certain weapons, like the sniper rifle, allowed such actions in first-person, but they were the exception. By and large combat and movement happened in the same top-down perspective as in the 2D Metal Gears. The camera was pulled much farther in on Snake, giving the player a more limited view of the surrounding space. This is what necessitated the various camera actions, to approximate (albeit with some new cinematic flair) the kind of spatial understanding that was effortless in earlier games.
Gameplay-wise the only new core actions MGS added were in hand-to-hand combat. Players could now grab, choke, and throw enemies. These new moves were useful because of another big change: punching was no longer lethal. Fisticuffs now simply knocked enemies out temporarily, which necessitated alternate silent take-down methods. In MG2 players could always punch enemies into oblivion if weapons failed. In MGS the same behavior would only delay a threat, not eliminate it. And since choking was a lot harder than punching, attempting silent take-downs in MGS generated a lot more anxiety. There were more possible outcomes, more ways to both succeed and fail than before. This, combined with the stronger need to observe before acting thanks to the camera limitations, gave the system largely inherited from MG2 a higher-stakes kind of tension.
Metal Gear Solid 2: Sons of
The stealth basics of MG1 and the expanded palette of MG2/MGS did not prepare you for the dense and subtle world of MGS2, which required a very different approach to problem-solving. You couldn't just run around killing everybody anymore, even if you did so quietly. Your strategy had to include removing evidence of your encounter. This catapulted Metal Gear into into a new realm of Hitchcockian suspense, as the game was now basically about the logistics of murder and not getting caught. Bodies were not the only evidence to be dealt with. Snake would now bleed when shot, leaving telltale trails of gore for soldiers to follow. Bandages would stop bleeding, but the easiest way was to simply stop moving for a period of time, further reinforcing the value of tactical stillness. The collective fury that would be unleashed on the player if caught made covering your tracks imperative. Engagements had to be kept on an individual level, to prevent group tactics by any means possible. The highest moments of tension were those between when the player was discovered and when the group was alerted. Unlike in MGS, where public alerts would sound the moment anyone saw you, enemies in MGS2 needed to communicate with HQ before the group responded. Killing an enemy just as they reached for their radio was a crisis averted, just as disabling a radio with a well-placed shot was a free ticket to make mistakes.
MG1, MG2, and MGS were fun little cat and mouse games, but MGS2 was really where the series opened wide as a possibility space. The number of dynamic outcomes involved in any given encounter, based on the various cascading levels of enemy behavior, was huge. More importantly, MGS2 required different types of thought and problem solving than previous Metal Gear games. Just because you were good at MGS did not mean you were good at MGS2. Enemy soldiers were different behavioral animals, ones which demanded private attention to be dealt with effectively. MGS2 is when your relationship with the enemy became intimate. "What do you do with enemies once you have them?" increasingly became the key question of the series, and as we'll see many of the big design changes (at least in the next two games) revolve around this idea.