Just some rambling below..
* A good game forces you to take difficult decisions.
There should be no obvious BEST choice of weapon or armor. Just a headache of dilemmas. Each weapon should behave uniquely and have inherent strength and weaknesses. Battle usefulness should decide the stats given to a weapon. (Not duels, since this is a primarily battle game.)
* "Sweet spots" of perfect builds together with armor should be avoided.
What I mean is that different builds, should be equally powerful. Ofc. it's not possible to make ALL builds just as good, but sound builds around the AGI-STR axis should be evenly powerful in Battle.
* There should be a reasonable balance between the classes. Both in: relative numbers of players, effort required, and power.
This is very hard, and it is too complex to calculate. It all boils down to experience and having a feel for it. You could argue that Archery is underpowered, but that the effort required is so low that an influx of newbie Archers would happen if you buffed it, changing the whole game experience for the others. Also there has developed different "Cultures" in NA and EU.
(At this moment, from my personal POV and from reading the forums there are some trends: Xbow/Archery and Cav and balanced inf builds are pop in EU, and STR and Pikes are popular in NA.)
* There should be variety. And the game should nurture what is unique about its nature.
Well here should be something about what game you want to make. Some ideology.
There are however some facts about what makes this game different from any other out there. The melee mechanics are at the core of this, and this is the single game I played the most in my life, and also the game that is capable of giving me the most adrenaline.. IMO the game should revolve around this.
I dunno why I'm writing this, but it feels like, and I can understand it, that balancers sometimes loose track of the big picture while focusing on details.
This goes to chadz as well. An all encompassing vision is perhaps what I'm searching for.