When you first start Super Mario Bros, the player faces a a very simple view. You find yourself as Mario, standing at the left hand side of the screen. Observing your surroundings, you see a flat ground before you with a bright sky and some hills in the distance. Your only choice is to move to the right, and so begins your journey.
It stands true that with most platformers, either retro or modern, your objective is to move from the left hand of the screen to the right. Like reading a book, players instinctively know they need to go to the opposite end of their starting location. Following this rule, game designers can be creative in how it affects a player's experience.
Let's once again take Super Mario for example. As you move to the right, your point of view moves as well. Suddenly, you see a mushroom you want traveling to the left, but just as you are about to get it, it travels off screen. At this point the player realizes that they cannot move back the way they came, the field of view has now become a physical barrier, and they have been punished for not reacting fast enough. In Super Mario Bros, the action of moving to the right can almost become it's own obstacle. It encourages players to be more aware of their surroundings, because you are only going to get one chance at using them to your advantage.
Other games may choose to let the player travel backwards, or to the left. One such example is in Kirby. In this sense, the game almost seems more forgiving. Perhaps you accidentally passed by an enemy whose power you would like to use. No worry, because you can find that enemy exactly where you last saw it. But what I noticed as I played Kirby's Adventure was that there was still a minor punishment. When traveling to a previous location, you will realize that all of the enemies previously encountered will respawn upon your arrival. Now simply heading back to swallow one guy becomes more of a risk as you can take more damage from many unwanted visitors. While this design choice makes it easier for players to absorb different powers, it still creates an added difficulty when you have to fight your way to the enemy you need.
Let's not forget that these games don't only force the player to go left to right. There is also the vertical dimension, where players choose exactly how they want to get to the other side of the screen. By traveling up or down, the player can reap certain rewards, such as mushrooms for Mario, or more food for Kirby. In some cases, this aspect will test the player's desire to travel right, like with a pipe in the middle of Mario's path. For those who know little about Mario, potentially sliding down that pipe may never have crossed their mind. In a way, the game uses this self defined rule of travel to trick the less experienced player into missing potential secrets, and challenge the more experienced to find them.
While seemingly simple, the approach to movement can affect different games and players in different ways. Moving backwards could be punishing in some games, yet a useful utility in others. Overall, one thing is always clear: I need to get to the right side of the screen.
It is interesting how such a simple facet, such as moving left or right, can have such a substantial effect on a game and gameplay. I liked how you read into the horizontal dimensions of Super Mario as both an obstacle and an incentive for players to become more aware of their surroundings. Maybe in having such simple mechanics, the game designer is also creating an emphasis on knowledge and mastery of the game world.
A very nice analysis of the horizontal dimension of game exploration. Talking about how the games incentivize vertical exploration also was a good choice. It's interesting that Mario, a character who is defined by his jump, does not do very much vertical exploration through in his first main game, and instead the player is reward for doing the opposite: crouching.