This post is going to try to address something that is a fairly old problem, but one that I feel a bit of a need to hash out, think of it less like a fillbuster and more me trying to put all of the arguments I have seen and felt in one location as well as some ideas I have for the new edition, and if anyone has any comments I'd like to hear them.
The main area that I'm looking at has to do with the relationship of the martial character and the caster, perhaps more than the caster and non caster. There are the common things about power balance, quadratic caster linear fighter, etc. What I want to look at is more the mechanical element as well as some of the...for lack of a better term cultural biases in this.
Alright, in summary the problems between casters and non had a lot to do with the vancian spellcasting system. The caster had a greater degree of impact per round and action than a non caster, in many ways able to neutralize enemies or end fights with a few gestures even at low levels. The theory was that this could be balanced by the casters relatively low HP and the limited number of spells per day. The problem was that the caster could usually stay out of reach of enemies since their spells had good range. The per-day limit was problematic too, if the game didn't have the assumed number of encounters in a day then the caster was technically a lot more powerful, able to unleash a lot more oomph. The other issue was that with scrolls, wands and staves casters were able to get extra slots and spell options fairly cheaply, especially when compared to the costs of weapons and armor for a martial character. In effect the casters money spent better too.
The other problem was that the martial character, or any non casting combatant really also faced the issue of enemies outgrowing them. Regeneration, damage reduction, great size, etc. rendered them harder to battle with normal weaponry and in many cases the monster was practically immune to any kind of combat stunt like tripping or disarming unless the combatant had effectively built their character entirely around that one combat style and even then it might be close. Mobility and the like were problems as well, to put it simply the caster outshone the non caster heavily in pre-4th edition.
It's worth noting that it wasn't just the wizard that was an issue here, the druid and cleric could outpace the fighter or nearly any other martial character at their assumed role. Hell, the druids ANIMAL COMPANION could outpace the fighter at their assigned role. There were other issues but those might need to be brought up later.
4th edition focused heavily on addressing the old problems, and to its credit they actually managed to (mostly) deal with them. The casters and non were effectively equal now with the new system. Roles were integrated and set up so that you didn't have a healing class outfighting a fighting class, etc. The fighter (often seen as the weakest class in 3.X) was now arguably the strongest. While this did help address some problems it also ended up creating a few new ones.
Some of the casters didn't quite feel right, you were mostly locked into your choices and the main use for a lot of the casters, the controller role, basically was removing mooks. Or they had abilities that would shut an enemy down hard (sleep, stun, paralyze) which could arguably have made them the key force but there were other things in the system that probably made that workable. 4th didn't work for my group, mostly because the combats went for too long and we missed the ability to modify and personalize characters as much as 3rd had offered. Looking at what happened though did lead me to some hypothesese that I want to share.
The problem that the fighter faces for the coming edition might be a problem rooted less in mechanics and more in culture. To put it simply, the fighter, the martial character, does not have the ability to commandeer the imagination the way that a spellcaster is. A magic user manipulates reality, they can summon creatures from beyond, forge illusions, blasts of energy, alter the world itself with a gesture. Time and space can be stopped by their command at higher levels, in essence, someone working on the design team can come up with ideas for dozens of spells and any number of them can seem reasonable and normal and become part of the game.
This gives the caster versatility and also a glut of options and variables. They can do things that a regular person would never imagine, and fantasy novels like magic because it works great as a catch-all to make something work. The problem is that the martial character often does not get this same level of space in the popular imagination.
The martial character is more likely going to be restrained by concepts of realism and shackles of 'normalcy'. This not only messes up the character in terms of ability but it also robs them of chances for development in supplements. There were a lot of feats in 3.5 for metamagic that let a caster reshape their abilities but there were few options like that for a martial combatant. The closest they came was with the tome of battle and tactical feats, though I will also give combat focus feats in Ph2 from 3.5 a nod.
The problem might well be this, look at a lot of the at-will abilities, simple hits with a weapon. It's more than simply swinging a sword, but for a lot of people the idea seems to be that the martial character just mashes the 'attack' button again and again and any variance from that is improper or unrealistic.
The tome of battle offered something a bit different, temporary surges in power, styles of combat that seemed to denote unique training, etc. A lot of the abilities looks different and felt pretty neat, and also sadly got ripped apart by people on the forums.
The idea that I have here is fairly simple, I want to suggest that they use something similar to tome of battle for the martial characters. My reasoning is somewhat less mechanical and more in terms of design advances. When a class looks exotic, when looking it over inspires people to try to make variants of sub-versions of an ability then the class will not only look 'cool' to people but it will also help provide ideas for designers. This way we aren't just pouring feats on a martial character and are instead giving them powers that they can use the feats to manipulate.
To the idea of 'realism' remember that someone that is well trained can perform feats that look superhuman. It isn't a matter of being magical, instead it's the idea that a person who has gotten this training has learned how to wield a weapon in such a way that they can do tricks with it that few others can. Consider that martial arts training can allow a relatively small person to overcome someone far more physically powerful simply by knowing where to hit and how to apply maximum force over a minimum spread.