For Spacebot, my current project, I've thought about a couple of weapon systems and ammunition methods, but settled on a solid approach to use.
The player will encounter (currently) six weapons through the course of the game. They have limited capacities, but can be reloaded by pressing the "R" key. Reloading is done through magazines, rather than a spare ammunition pool (which has become the de facto standard -- more on that later). Reloading uses one magazine in inventory, and any remaining loaded ammunition is discarded.
The current weapon list follows. The descriptions should be straightforward except "Vacuum", which represents whether a weapon can fire in open space. (There's no oxygen, so weapons relying on an explosive action won't work.)
Capacity: 10 (unlimited reserve magazines)
A semi-automatic laser pistol. Fires one shot in a given direction.
Cyclic Rate: 750 rounds per minute (12.5/sec)
A fully-automatic projectile weapon. Fires a rapid burst of metal slugs forward.
Power: Variable (12-96)
An energy pistol with a charge function. The longer a player charges the weapon, the more damage it deals, but also the more ammunition it uses (anywhere from one to eight charges).
A short-range dual-fuse grenade launcher. Fires in an arc forward; the grenades will detonate in two seconds or on impact with an enemy.
Power: 5 (times 6 shots)
A shotgun-style weapon that fires a spread of needle-like flechette projectiles forward.
Capacity: 5 seconds
Power: 150 per second
A flamethrower-style weapon. Fires a powerful jet of blue-hot plasma in a short-range lance.
(As an aside, any readers familiar with Bungie's Marathon series might recognize a few of the weapons in there -- I confess I did get some inspiration from there.)
The goal for this game's weapon set is to provide the player with a varied arsenal of tools, none of which duplicate another's function. I've thought carefully about the weapon set, and I want it to fall in line with Spacebot's overall design goal -- keep the game fun, interesting, but simple. Don't overwhelm the player with choices.
Therein lies my first conundrum -- does the Flechette Gun duplicate the Plasma Lance's purpose as a short-range power weapon? I've been thinking about this for a while, and I've come to the conclusion that it doesn't, and here's why. The Flechettes are designed to be wide-range, and allow the player to hit targets without precise aim. You may note that the overall maximum power of the gun (30 points) is quite small compared to what you might "expect" a shooter's shotgun-like weapon to have -- this is also by design, but more on that in a moment. The bottom line is that it is not a "power weapon" by any stretch of the imagination.
The Plasma Lance, however, is tremendously lethal at close range, but deals no damage at long range (the weapon simply doesn't reach that far!). It could be used in situations where the player wanted to hit several targets in a wide range, but he'd have to do some complex maneuvering to get that to work.
Why do I carry on about the notion of the weapons not having duplicate functions? I believe that having several weapons doing the same thing adds complexity -- that doesn't mean it's wrong necessarily, but it does depend on the overall aesthetic you're going for. Here are a few systems and some discussion of examples.
Take a look at Marathon, the game whose weapon system I'm probably closest to. That game had the following array of weapons:
Assault Rifle/Grenade Launcher
The only weapon that needs explaining is the "alien gun", which was a rapid-fire weapon that shot from three barrels in a spread pattern.
The principle of this game was similar -- don't duplicate the effects of any one weapon in another. The only two weapons whose functions are similar are the grenade and rocket launchers; the difference is in their deployment. The grenade launcher is a tactical weapon; it has an indirect fire arc, and can rapidly shoot seven grenades per load, but the grenades are low-yield with a minimal blast radius. The rocket launcher was a two-shot weapon reminiscent of the same weapon from the Halo series (in fact the Halo launcher was more or less a copy of Marathon's, with the same name and all!); it has a very wide blast radius and deals significant damage, but is slower, and has a direct fire line.
Jet Force Gemini did this too; there was an array of about 20 weapons to choose from, but each had its own purpose and none duplicated another.
The rationale behind this system has already been explained; let's compare it to another system.
Large weapon array
A large number of shooters in the early 3D era (roughly around the time of Quake II) had, as selling points, a bewilderingly large array of weapons for the player's use. The consequence was that a lot of them did largely the same thing. This system leaves a lot more room for interpretation, because there are a few reasons for including a huge array:
Duplicates of increasing power: Wolfenstein 3D used this system, and it's the most basic example thereof. The player had three projectile weapons: a pistol, submachine gun, and gatling-style gun. Each one used the same ammo, dealt the same damage, but had a progressively higher rate of fire than the previous one. This gave the player a sense of progress, as his gun got badder and badder and he became more effective in combat. Once the player acquired a weapon, he wasn't expected to use the previous one again. This rationale can be applied in other games, too -- Doom did this with its pistol -> chaingun combination, but the system broke down when it introduced the plasma rifle, another rapid-fire machine gun weapon, but which was clearly superior and still used its own ammo; could the game not have dispensed with either the chaingun or the plasma rifle entirely and just kept one or the other as the "machine gun" weapon? The pair of shotguns from Doom II is more in line with the theory -- the "super shotgun" dealt triple damage despite only using two shells, and had half the rate of fire of the basic pump-action.
Sheer quantity: You saw this in some games, like the original SiN. Having 20-some weapons was nothing more than box-copy, and was supposed to be a selling point. A less materialistic interpretation came from Ratchet and Clank, where the player obtained dozens of weapons with their own ammo and purpose, but the quantity was built consciously into the game's mechanics rather than as an afterthought. The whole point of the game was the accumulation of an arsenal -- it was a means to its own end.
Limited Inventory: The most straightforward example of this comes from most present-day shooters in common circulation. The Rainbow Six: Vegas pair of games is a fair example: there are at least four of each "class" of weapons (handguns, shotguns, assault rifles, and so on), but there is no way to determine which one is necessarily "better" than the rest. It's usually a matter of personal taste. However, since the player can only carry two primary weapons, he isn't forced to slog through a massive inventory to find the specific piece he wants. He's forced to think, tactically, about which variation on the assault rifle is best for the upcoming combat scenario. This is the system I'm most willing to accept, because even though there are weapons that duplicate each other, the player would be silly to carry a pair. What use is having two pump-action shotguns, for example, if you can't engage targets at range?
The large arsenal theory makes some sense in each of those decisions, but it can be dangerous in some cases. If the player accumulates many weapons quickly, he will eventually come across a weapon that is "best" -- something he uses, constantly, in just about any circumstance. Give him enough ammo for that weapon, and he'll never touch anything else. It's an extension of an issue apparent in some fighting games: the "power move". Give the player, say, twenty unarmed combat techniques, but put in one that deals an inordinate amount of damage with few drawbacks. It's the only move he'll use; the rest are wasted code. You essentially have two options at this point: 1) Weaken the move so it's more in line with the rest of the options. Say, decrease its damage, or increase its recovery time, or provide some other sort of disadvantage to it. Or, 2) Remove the other moves that compete with it. Sometimes this can be the better option; if the player always uses one weapon, build the game around that weapon and ignore the rest! It's purer and gives the player fewer extraneous details to suffer through.
So there you have just one of the litany of thoughts that go through my mind with respect to game design and how I can apply lessons learned and overall feel to the games I design. More to follow.