My personal pet peeves of the d20/D&D game system:
in no particular order of preference -
- the magic fire-and-forget system. I've read novels, seen movies, read other rpgs, read more novels, and I have never, ever seen this system or style of magic utilized (I've not yet read any of Vance's original novels, which is wheret his magic system comes from, but why in the world give so much credence to this outdated and rather hasslefilled magic system that is about forty or so years old).
This magic system is bland to me, and doesn't make much sense logically.
- prestige classes. I've yet to be in a d20 game where half the players will sift through any books looking for prestige classes to become, aim their characters in that direction, and despite any story changes or character decisions in the story the player pushes the character along a path that not only does NOT make sense but is pure meta-gaming from the moment the character is created. I wish the core rules had a ruling or option for changing how prestige classes operate and can be attained.
- the x/day abilities. I can understand why this is done...it keeps the players in line. But, lets compare Rage to Sneak Attack. Rage is limited per day, which is assumed to be about how many times per day the character might get involved in a hard challenge encounter (I'm assuming of course, I could be wrong, first time for everything

). Sneak Attack is not limited, based on situation, the rogue could sneak attack all day long without limit. In the long run, which is more powerful.
Plus, by having these limits, players would sometimes make choice that just don't make sense. Have a barbarian hold back his rage in one combat because "the next combat might be harder" so he chooses not to use it, not because of an in game reason, but because of meta-gaming thinking.
- no background options. d20 Modern does this in spades, as far as occupations and background go (I think).
- combat. This take too long. Too many options, too many tactical decisions made by players who count the squares, decide if going the full 30 feet is wise, think some more, count in another direction, try to evade AoO's, see which enemies threaten which squares, where should the center of a spell be so he doesn't hit the other party members, which spell to use, keeping track of all the feats, which character provides the group with what bonuses, how many hit points to keep track of, players making decisions that are bogus and completely made due to meta-gaming, etc, etc, etc.
For a game in which the combat rounds are simulated to be six seconds, if often takes a good hour or two to complete a combat that lasts no longer than 8 to 10 turns (which in my book is just one minute of game time).
I think this is about it for me.