Our discrete history
Before about 1995, video games almost universally used discrete controls. The classic boxy Nintendo Entertainment System controller is a perfect example, it had a D-Pad with four directions (plus combinations resulting in diagonals), select, start, A, and B buttons — 8 in total, each being either ON or OFF. The video game industry created games that took advantage of these controls, and for most of its history, home console game engine design was directly influenced by these restrictions.
Analog controls have been becoming increasingly popular over the last ten years or so. Most game controllers have analog sticks built-in these days, but Nintendo is really leading the charge with the Nintendo DS and the Wii. The Nintendo DS uses a touch-screen and stylus in addition to discrete control buttons that are similar to the Super NES layout. The Wii, meanwhile, has attempted to re-invent console gaming with accelerometer controls and a pointer in addition to an analog stick and discrete buttons.
When used correctly, analog controls bring a stunning new degree of freedom to a game. They provide the opportunity to run or walk at various speeds, aim quickly and easily at any arbitrary point rather than only the standard eight directions, and provide an element of fine control that was, in the past, only clumsily simulated with buttons that would only move either too fast or too slow.
Unfortunately, game design has been influenced by discrete controls for so long that designers are having trouble shaking off old habits. Controlling discrete actions with analog devices is simply a hindrance.
Emerging analog elements
To illustrate my point, I'll use Nintendo's critically acclaimed Wii version of Twilight Princess, part of the massively successful and long-lived Legend of Zelda franchise. This game did several things right, and a few things wrong, with the analog controls.
First, the right things. The game's protagonist, Link, is moved around with the analog stick. This works extremely well, because it allows Link to move in any direction with relative ease and provides multiple levels of speed and fine control to work with. Likewise, the game uses the pointer to aim various ranged weapons such as the Boomerang and Bow & Arrow, providing a level of intuitive precision and speed that was formerly only available with a computer mouse, and in fact has probably surpassed it. Simply point the remote at the thing you want to hit and push the button.
The discrete controls are left over for most discrete actions, that is, actions that neither have nor need degrees of precision to execute. Once the ranged weapons are aimed, firing is done with a button push. Picking up rocks, targeting the closest enemy, pulling out items such as the lantern or bottles, and slogging through dialog boxes are all done with discrete buttons, as they should be.
The problems arise, however, on those occasions when the player must control discrete actions with analog controls.
Don't get me wrong, Twilight Princess has come closer than any other game I can mention to doing this appropriately. That's what makes it such a good example. 90% of the time, you'll get the results you wanted. But when compared to the practically 100% accuracy of using discrete controls in these situations, it can only feel like a step backwards.
Twilight Princess controls the following discrete actions with analog motions:
Normal sword swings and thrusts
Done well, this actually increases the player's immersion in the game and makes the controls intuitive and easy to remember, which can excuse a small loss of accuracy. The sword attack, for example, is done by merely swinging the remote to the side. Hooking and reeling in a fish — in both versions of fishing available in the game — have you use the remote almost exactly like you would use an actual fishing rod. Compare this to the bizarre button combinations required in Ocarina of Time (e.g. hold B and R to reel the line in faster) and it's clearly the superior format.
Done poorly, however, it simply becomes frustrating. The shield attack and spin attack are both performed by shaking the nunchuck controller, in two different directions. The problem is, unless you're holding the controller perfectly level, the game can easily mistake a shake in one direction for a shake in the other. In this particular case, it's a big problem, because the shield attack is used to open the enemy's defenses while the spin attack leaves Link open to counterattack. So the mistake is most likely to occur at a moment when the enemy is most ready to take advantage of it. This was never a problem with most button-based controls, even ones requiring Street Fighter-style combinations to execute (which quickly became muscle memory).
The difference, it seems, is in similarity of the controls. The normal sword swing is entirely unlike any other action performed with the remote when you want to swing the sword. It's extremely unlikely for the game to mistake your intention, even if 75% of your effort looks like a sidewise swing and 25% looks like a vertical swing because you weren't holding the controller perfectly level (which, of course, defeats the purpose of the attempted player immersion).
Games that also have big problems in this area include the remake of Rampage for the Wii and the Boxing game included with Wii Sports. Neither one of these games really required any analog controls whatsoever, and trying to shoehorn them in left them both with playability issues. Boxing has trouble registering the fact that you've attempted to punch, or understand what kind of punch you're trying to throw, while Rampage suffers from a similar problem to the shield attack/spin attack confusion in Twilight Princess.
One bright spot in this gloom, however, is the remake of Punch-Out!! for the Wii. While the game does, in fact, support analog controls, and even the Wii Fit balance board if you've got one, they are entirely optional. In fact I'd be very surprised if anyone chose to use them for the single-player portion of the game, as it's really not suited for the style of play at all. Punch-Out!! is and always was a discrete game, not an analog game, requiring split-second timing, memorizing patterns, and making use of a mere five options for attack (left and right punch, left and right jab, and uppercut). Where the analog controls would be fun to use is likely to be restricted to the two-player game. Both players, if using the analog controls, can't help but feel more like they're really sparring against each other rather than seeing who can push buttons faster.
Our analog ancestors
Given the choice, however, I'd much rather be forced to use an inappropriate analog control than an inappropriate discrete control. Unfortunately, engineers fell in love with pushbuttons in the 60s and have been trying to use them wherever they could ever since (anybody remember the pushbutton car transmission?). The problem is that pushbuttons, however cheap, reliable, and easy to program they might be, are incredibly limited control devices. They simply cannot compete with analog controls in certain applications that evolved from the analog era.
Take the common television for example. Practically every television remote control on the market has nothing but pushbuttons all over it. Dozens of them, in fact. But if we look at the volume control, we see it can only adjust the television's volume at a certain speed, and that speed is usually "slow". So what? You ask, how fast do you have to adjust the volume anyway? Well for one thing, you wouldn't need the "mute" button at all if you could turn the volume all the way down with a flick of the wrist, and secondly when Casablanca is interrupted by a commercial for Crazy Eddie's Used Car Sales, the faster you can adjust the volume, the better. Likewise, buttons that toggle between multiple settings (e.g. video inputs, widescreen formats, etc) are much better done with switches that can be flipped to the appropriate setting immediately than buttons that cycle through all the available options, one at a time (although on-screen menus are a decent compromise).
The classic switches and dials from the analog era of expensive, delicate vacuum tubes and trimpots acted like an extension of the user's will (or at least, they did when the notoriously finicky devices were working correctly). Adjustment took place at the user's convenience and comfort by default. But these behaviors are difficult to simulate in the digital era, where analog inputs are expensive, both in terms of processing power and design time.
Buttons are a one-size-fits-all compromise that can do everything, and cheaply, just not very well. Although they do have one significant advantage in providing multiple control locations. Multiple switches, for example, only work well in very simple applications such as three-way light switches. Imagine if your television had an input switch rather than buttons on both the television and on the remote. What if one was set to "Cable TV" and the other set to "DVD Player"? It's a situation that invites paradox and confusion.
Developers need to step up to the challenge
The point being, of course, that using the correct control for the application makes an enormous difference in the usability of the product. But the flexibility to choose your own input methods isn't always there. Game developers for the Wii are restricted to very few discrete buttons for user input, and DS games seem to be forced by Nintendo to make use of its various features such as the touchscreen and microphone (which makes sense in a way, otherwise these features would likely sit unused as developers stuck to their comfortable old ways).
And the Apple iPhone has no usable, tactile discrete inputs at all (the buttons that do exist are restricted to OS functionality and are not available for application use). Of course it's possible to include touchscreen-emulated pushbuttons, but with no tactile feedback it's difficult to keep your eyes on the action and on the buttons at the same time. The iPhone was developed with analog and touch controls in mind — exclusively — which makes it difficult for game developers to port existing video games to the platform, especially action games.
But a revolutionary platform requires revolutionary thinking about how to design to its strengths, and this is where developers are falling short with today's analog devices. Rather than developing for the device, they're trying to force old ways of thinking and controlling into a new, and largely incompatible, format. Finally granted the freedom to break out of discrete ways of thinking, they have failed to embrace the potential that it presents.
Take the Super Mario Brothers franchise, for example. Since its pre-Super days of Donkey Kong and Classic Mario Brothers, the franchise has had a discrete format. Characters, enemies, and levels were, and to some degree still are, designed to fit in unit squares. Running, jumping, and attacking are still largely discrete actions, with little, if any, analog variation. Why doesn't swinging the Wii remote faster make Mario jump higher? Why can't you throw fireballs like a baseball pitch (imagine the possibilities for throwing enemies a literal curveball!)? Why can't Mario put up his dukes and box? Or catch Hammer Brothers hammers and throw them back? Or any of a hundred other actions that motion-sensitive controls make possible? The franchise is mired in its roots from its humble, discrete beginnings. Super Mario Galaxy has done little to advance the possibilities of its controls since Super Mario 64 introduced variable walking speeds via analog stick. Nintendo developed the Wii, and they need to take the lead in showing third party developers how to take advantage of it.