A character with no skill in anything would be quite hard to play. The numbers are stacked against such a character; starting stats and skills tend to be just enough that most players will need to rely on class-specific abilities to get a leg-up on the monsters. These skills make possible the character’s engine, the system by which he kills monsters and earns experience within acceptable levels of risk. Having an engine is not strictly necessary, and for some race/class combinations is as simple as walking up to monsters and hitting them with stuff, but without one the player will have to resort to making use of random items and extreme tactics more often, strategies that bring with them necessary dangers.(Italics mine.) This idea of an engine is an excellent piece of terminology when we think about the design of tactical games. As soon as part of your aim is to provide the player with different playing styles, different ways of going about combat, you will want to ensure that the game allows the use of different engines. This may sound obvious. However, it is hardly ever done.
Game designers almost always realise that they need to diversify the game, and to this effect they put in different classes, or races, or types of equipment you can find and use. But they rarely realise that this diversity amounts to little if it doesn't add up to different engines, different ways of playing the game. Let me give you some examples from Dungeons & Dragons 3.5, a game with which I am familiar enough and which is perhaps not entirely unknown to most of my readers.
Let's call the system of walking up to an enemy at your maximum possible speed and hitting him with an attack every turn the basic melee engine. Numerous classes use this engine almost exclusively, including the barbarian, the paladin, the fighter, the non-ranged ranger, and the monk. So what have the designers done to vary these classes and change their engines?
Well, they have done a lot to vary the classes, but few of these variations actually change the basic engine.
- The barbarian's illiteracy and trap sense have little effect on combat; his uncanny dodge, improved uncanny dodge and damage reduction are passive abilities that make him survive a little longer but do not change his strategy. Fast movement has some tactical relevance, but will only rarely make you do something you wouldn't otherwise have done. Finally, his signature rage ability only locks him further into the basic melee engine: once activated, the barbarian hits harder, and loses a couple of combat options he probably would use anyway.
- The fighter has two specials: he is the only one has really specialise in weapons, and he has a lot of bonus "feats" -- which makes him a bit like a pick-and-choose class. The specialisations are merely a passive bonus without tactical import. The feats are more interesting: some of them actually do change the engine (the mounted combat tree, things like "improved trip" which add combat options, to a certain extent things like "whirlwind attack" which require you to wade into the fray).
- The monk has lots and lots of specials -- and almost none of them make a difference to the engine. You can attack without weapons, you have a multiple-blow attack, you get armour bonuses (to make up for the fact that you cannot wear armour), you get vast amounts of passive resistances -- fine, but walking up to someone and hitting him is still the only viable thing you can do.
- Let's look at the paladin last: again, lots of passive resistances, some healing capabilities that are hardly different from having a potion of cure wounds in your inventory, and at higher levels a few minor spells. Once again, you have little choice but to walk up to your enemy and hit.
It seems to me that any interesting combat game that is either long or wishes to be replayed will need to give the player the choice between multiple engines. What's more, you need to make sure that the things you are putting into your game either enable new engines, or tie in with them. Implementing poison that continues to deal damage to a monster once he has been poisoned is fun even when its just a nice little bonus during your fight; but it becomes much more fun if it enables new tactics, such as a hit & run tactic where you poison some one and then run away, only to come back later when the poison has done its work. Or a hybrid weapon/magic-tactic, where the player poisons his enemies and then takes advantage of their lowered magic resistance (assuming that poison works this way in the game). Or even a hybrid weapon/diplomacy-tactic, where you poison someone and then tell them that you yourself are the only person who knows the cure!
I tried to make a small example of different engines in the ATTACK test dungeon. Combat using the dagger and the cloak of shadows is quite unlike combat using the mace: instead of the back and forth of attacking, defending and concentrating, there is the slowly rising tension as the player decides whether or not to risk another turn of observing the target... and the mad dash out if the attempted assassination fails.
Another matter for careful thought is the availability of engines: you can have the player switch between them at will during the game; you can make him choose in advance and lock him into that choice (i.e., choosing a certain class); you can have him develop skills, such that at a certain point in the game he is more or less locked into the engines he has chosen to develop; and so on. Here, I would intuitively think that locking someone into an engine is the less interesting choice, motivated more by a desire for easy "balance" than by something else.