While hurting my head with hair mechanics, I've thought a little bit about games where you move around a world.
I really love moving through a world. Crackdown was a good game to me, because running through the city was so damn fun.
In the prototypes I've created, I've found a few things out.
The biggest is that - shock - your world needs to be lumpy. That is, it needs to have lumps with very different flavor from each other. I think some people really underestimate this. It's a bit more complex than it looks.
First, the regions of the world have to look distinct so the player will be able to remember the various regions and know what to expect when they enter an area. This can't just be a visual change: the nature of the topology has to be different, so that each area feels unique to be in.
This is one reason I don't much like games where driving around is the primary method of getting around. Driving doesn't really feel that varied, and you can't easily look around.
There's a lot of different ways of getting around, and it feels like folly to try to make basically all your methods of getting around variations on the exact same basic method.
So the thing I've discovered: The world map isn't defined by the stuff in it. It's defined by the way you move through it.
So, obviously, when we talk about the way the world varies, we should vary it by changing how you move through it. More than that, we can combine various methods to allow you to explore along different grooves and get different views on the same areas.
For example, let's say our character has motorized roller blades. The state of the road will therefore matter, and we can create unique ground paths by varying between straight roads, tight roads, stairs, slopes, grass - all of this will change ground travel.
But we can also talk about the high travel across the rooftops. Here we can talk about dash capability on long roofs, traveling across beams that connect the roofs, leaping from roof to roof fluidly, leaping and catching a ledge, climbing sides, controlled falls, slides, and catapulting... these all lead to a different kind of groove, a different level of open-ness, and a different fundamental feel.
So you can build your city by mixing different ground and air travel types. Now, the key is that you don't say "zone 13 is parkland and smooth-jump". Instead, you use the various methods to work at odds. So "zone 13" might have parkland and smooth-jumping, but they would be crossing. If you were currently doing the smooth-jumping, you would be exploring in a different direction and seeing things from a different angle. Basically, this allows you to have the player treat the same space in different ways, moving in different directions, seeing different things.
But that's just the tip of the process.
What about vehicles? Well, cars and bikes aren't very useful because our character has magic roller blades. But there are other options. Gliders, sky rails, cannons that fire you at angles of your preference... There's also the option of underground travel, although this is done best with "open" undergrounds rather than sewers, because you want the player to frequently see the buildings and areas he knows from above ground.
Sky travel is frequently long-range, so we need to understand that when using it.
There's also different world modes we can explore. Night vs day. Rain verse clear. Spirit world versus real world. These can change the player's capabilities, the world's nature, and so on.
These days, most open worlds have very large worlds. I would actually prefer smaller worlds with higher density, and these different world modes open up a very easy way to increase the density. For example, in the clear day, the massive solar wings extend on many of the buildings, changing the way the high travel plays. In the night, the buildings retract slightly, conserving heat.
And so on.