There exists no more rancid a pustule and blemish upon the mechanical mores of our hobby than the modern D20 systems. In fact it is well within acceptable boundaries to posit that their continued existence and market dominance is an affront to God himself by the defiance of good iterative design principles alone.
Many proponents of D20 systems hide behind assertions that people can like what they like. This is certainly true, to an extent. However, a role playing game system exists to facilitate a unique art form, and can and should be critiqued on the merits of its ability to accomplish this.
So how exactly do D20 systems fail in this regard? The short answer simply is that they lack any sort of coherence. Rather they contain nearly 40 years of ossified thematic and mechanical incoherence that systemically works against anyone wishing to coherently theme and tie together a story within them. Lets consider an example from the systems themselves.
What would one conclude are the core themes of a generic D20 system if they simply read over the necessary rules of play? I think they’d certainly have a hard time paring down a list from the myriad of things the system touches on. The armor class system indicates that the game is intended for heavily armored melee combat where one must hit an opponent’s weak point to damage him, but the wide selection of weapons and armor contradicts this. The levels in minutia in terms of gear weights and carry limits, need to pedantically determine the amount of things and implicit need for pedantic item accounting as well as the magic system point to a significant emphasis on forward planning. The emphasis of character advancement on increasing combat effectiveness in turn suggests a major combat focus as well.
Now, in all seriousness what do we call a game with a limited type of combat focus, forward planning, and largely concerns itself with martial engagements? A wargame. Which of course makes a lot of sense, D20 was evolved out of in depth grid based wargames of the 70s and early 80s. For those of you who you haven’t spent inordinate amounts of time researching the history of traditional games and older games, I’ll try my best to explain and simplify the implications of this relationship.
Back before the popularity of D&D, wargames were the thing to play. The hobby was a lot smaller back then, and tended to be dominated by the then industry giant Avalon Hill (RIP and God Bless). Avalon Hill and others made wargames, but they weren’t anything like what you see today. These wargames revolved around scenarios created by the writers, cardboard counters for units, grids, and were quite often highly asymmetric. Detail and simulation were given precedence over mechanical ergonomics and ease of play. This legacy has largely been left behind by modern wargames, but lives on in D20 rules.
One of the characteristics of early wargames was that designers wanted to stat and rule anything and everything that could conceivably come up in the system. This was fine and good back in the days when a wargame was just about submarine combat in WW2 or a single battle or campaign. But when you export those mechanical design sensibilities to a game that could theoretically cover just about anything, you end up with a tendency towards making a bloated mess.
I do not mean to impugn early iterations of D&D, they remain significant works for the hobby, and at the time their design principles were cutting edge. However, for a variety of reasons, the subsequent designers of the system failed to improve from this basis, largely due to corporate pressure and a simple lack of the genius of Gygax himself.
This tendency to attempt to quantify every interaction within the system is the largest weakness of the D20 systems generally. Rather, it creates systems bloat. This isn’t to say every single individual D20 system has or tries to have rules for everything, but if you gave the developers enough time, they would give it their best shot. All systems that inherit the legacy of D&D inherit this design philosophy in some sense, adjusting class balance, random tables, and skills somewhat is just too easy to make new editions I suppose.
There does come a point where the actual point of a tabletop role playing game comes into question. How can one exactly claim attempting to create mechanical solutions for every problem is necessarily bad? I would suggest the metric best used is to what degree do these elements facilitate the ultimate goal of a table top role playing game. That is to say, is this well designed for the end user or not?
The ultimate goal of any table top role playing game is to facilitate group story telling, and within this context the rules serve as an arbitration mechanism for disputes that cannot be reasonably handled between parties. This, of course, is the barest necessary components for such a game, and everything you see in games comes from these components. D20 doesn’t rectify these two at all. In fact one can argue quite well that D20 fails to have basic system ergonomics lending it internal mechanical consistency (on a side note, my best example is the continued inclusion vestigial ability scores as opposed to simply having ones stats be their modifiers).
Of course D20 systems have endemic issues outside of their own mechanical clumsiness. One great example is the inherently hostile nature of game master player interactions. The wargame roots of these systems and subsequent culture that has sprung up around them fosters the idea that the game master is out to get or trick the players. How is a group supposed to tell a story when the fundamental assumption of all interaction is hostile? Long story short, they don’t. They play an in depth wargame with shopping segments. Or put simply, a wargame for pansies.
Of course this all lends me to ask the question, why should I play D&D when I could have a more balanced and fulfilling experience with a small squad wargame? I could link those engagements together into a small albiet cohesive narrative. Eventually, at some point, every playgroup asks themselves this question, in some sense, and they come to their answer. That answer usually is to excise large portions of the system or ignore them. Seriously, when was the last time anybody used ALL the tables, charts, tiny rules, and tables upon tables of modifiers to simulate a vancian magic fueled medieval kitchen sink?
Sure, there is a skeleton of an enjoyable system somewhere in there, but that isn’t the question asked. I can buy a yugo and completely overhaul it, give it a different engine and like my yugo. But my doing that doesn’t make an off the lot yugo any better. Same for D20, if whats in the book falls short, it falls short, simple as.