A recent resurrection of my Gunplay post has led me to thinking. Perhaps it is time to summarize.
Recently I've been talking a lot about navigating the world. In my opinion, if you base your core gameplay around simply navigating the world in fun ways, you'll have a hit on your hands.
Examples abound. Skate lets you control your body and your board in an intuitive way such that moving around and doing tricks feels exceptionally natural. Crackdown makes climbing buildings and leaping from roof to roof excessively fun. Even in some not-so-spectacular games - like the recent Hulk and Spider-man games - the reviewers note that the game was fun until it actually started. Because it was fun to move around.
And, of course, Katamari.
There are also a lot of games where moving around is just a way to get from gameplay element to gameplay element. Most games are like this. Moving is important, but it's important because it lets you get behind cover, or reach an enemy without stepping on a land mine, or lets you push colored blocks into colored holes, or whatever. That's not deep navigation: that's shallow navigation. It can give you access to a fun play element, but it isn't, in itself, a fun play element.
On the other hand, games like Crackdown, Katamari Damacy, and Skate let you establish a close working relationship with the world around you. A random ledge is not simply something to use as cover or bypass to reach a better location: a random ledge is a place to grind a sweet trick, or a loose thing to collect when you're big enough, or a great place to grab on your way to the top of the building... the ledge itself can host gameplay. Of course, what things are considered elements of the world will vary on your game: Skate has no loose debris, whereas in Katamari most of the level is loose debris of various sizes.
An easy way to determine the depth of your navigation play is to ask yourself, "if this was an empty plane with a ledge/a ravine/a signpost/litter/etc, would it be at all fun?" If your answer is "no", your navigation is transparent and not deep at all.
Which means you'll have to work extra hard on the rest of your game.
Navigation certainly isn't the ONLY kind of play in your game, after all. (Unless you're doing a casual game.)
Every sizable game has other kinds of play that merge nicely with the primary play.
In Skate, you run around getting sponsors and competing and so forth. This is a great way to push the player to try new tricks in new places, showing off just how diverse the navigation can be. It also lets you make your skater look nice.
In Crackdown, you do a lot of shooting and punching people. However, your ability to shoot and punch effectively is directly related to your ability to navigate: things are safer on rooftops and you have an easier time getting the drop on people. Crackdown also has mission play where they twiddle the combat play. Even though the mission play actually screws up the game, because it's so fun, it's forgivable.
In Spider-man 3, you do a lot of swinging from a thread. However, unlike Crackdown and Skate, the other play loops don't really show off new and interesting ways to swing from a thread. Fighting involves NOT swinging from a thread and instead just punching large numbers of people. Missions are pretty bad, too.
How can you tell whether another play style augments the first? It's actually pretty easy:
Does the second play style push the player to play the first play style in new ways?
In Spider-man 3, fighting doesn't push you to navigate in interesting ways. In fact, it basically forces you to NOT NAVIGATE AT ALL. While it's part of the franchise (Spider-man always fights villains in the comics), from a gameplay perspective it's actually worse than simply not including it at all.
In Crackdown, fighting and missions usually reward you for finding weird back entrances, climbing high spires, scaling rocks, tightroping across pipes... while fighting (ranged or melee) itself doesn't include much navigation, the way it is integrated into the levels makes it require navigation before you even start.
Of course, Skate is kind of the ultimate example, because every mission is specifically to push you to navigate in new and interesting ways...
And all these feed back, too. Being better at navigating allows you to fight new battles in Crackdown. Being better at navigating lets you accomplish missions and get new missions in Skate. Being better at webswinging in Spider-man 3 gives you... NOTHING. Absolutely nothing!
Regardless of the play you want to augment, this argument holds. If you're making an RPG and you want to augment the battle play, you make a kind of play that encourages players to battle in new and interesting ways. This could be new and interesting enemies, new and interesting battlefields, new and interesting player capabilities, or a combination thereof. Obvious examples are progressing plots, gaining levels, and buying new equipment. Similarly, battling in new ways will unlock more plot, more levels, more equipment...
I think it's a pretty simple way of looking at things.
Is it clear? Can you break your favorite games (or least favorite games) into these kinds of linked loops (or notice the fail points of their linkages)?