Hey good theory. Mobility and the ability to transform it in to whatever you want, it's almost like expression. At the same time its the fun of danger (?) like being able to dive off high platforms, a thrillseeking. But you know what I mean when I say run dive flip long jump (dive in the middle) and shoot right through a hole in the ground. It feels great, i'd even say it's a feeling of accomplishment just as much as nabbing the star.
hmmmmm *think* mobility, complex in motion, *designing* your own *method* - to *experiment* in *control* ACK! I need to play with this.
*does so*
*looks at porn first*
Actually restricting movement in certain ways adds to it as well. I think the trick is giving the player enough mobility to give them a sense of control and removing enough to provide a challenge. On thinking about it, I find that a lot of the time restricting via the environment and the enemy is a lot more satisfying than those methods that just null out your abilities like "mute" or something. In spite of how cheap a trick it is, it's amazing that something as simple as reversing one's controls as a nerf adds to tension and relief when one finally adapts to the situation and is fully capable again.
Actually on thinking about it this mobility thing transfers to other games in certain ways. I might be overthinking it, but maybe instead of mobility I should say the important thing is providing the user with a multitude of options at any one time. In an RPG, say Chrono Trigger, the positions of your characters are locked. That's not mobile at all but I still get a sense of freedom as I'm able to select all sorts of strategic options in defeating the enemies. Further, the more "interactable" a world is the more a person gets the impression they have some freedom to do things. A hallway is boring, but a maze is great. More importantly though, here's the fun thing about a Mario game. Even if you are utterly powerless, you are allowed to try everything you've learned to do anyway. One frustrating thing about this or that game is not being able to "at least try". That is, they strip you of freedom by reducing the discovery that a door is stuck until you get the right key into a cutscene or a message you get on examining it. In, say, Zelda, you can smack your sword on the lock over and over again. You can bomb it, hammer it, "arrow" it, use Din's fire, play a song, and all that stuff. If you are allowed to use your abilities, even if they won't work, you create hours of a sort of fun.
ABF actually touches on this now and again, but if a game lets you at least try your fire spells on a door instead of only on undead, there's a much richer experience. FFIV comes to mind. In that game, numerous times you find odd things and an inventory window comes up allowing you to try whatever you can think of. Not only does this allow a puzzle element, it adds to a sense of the user actually being free to do things in the world, even if, say, there's these two kids that are turned to stone and technically there's nothing in your inventory you'll ever get to de-stone them.