Let's assume, hypothetically, that a new revised edition of the D&D game were being produced. What follows is a list of technical and terminology changes which I would strongly suggest making -- in general, they wouldn't actually make any effective changes to gameplay, but would make the concepts involved clearer and easier to organize.

I. "Attacks of opportunity" become "openings"

For a mechanic so central to the play of combat, "attacks of opportunity" have probably the longest and most unwieldy label in the game (most writers resort to referring to them as "AOO"s). Switching to the word "opening" shortens any references, and still alludes to the old "opportunity" label. Defenders can "give openings", and attackers may "take openings".

II. Size categories are revised

A very few minor edits to the creature size category table would make it easier to read and organize. The first is that the eyesore "Medium-size" should become "Medium" for the obvious advantages of brevity and consistency with the other size category names. The second is that, in English, the size categories are almost ordered both by length of category label (counted in both letters and syllables) and reverse alphabetical order (which would be wonderfully convenient for database and spreadsheet sorting functions); altering just a couple of the names will help to crystallize that. At the large end, "Gargantuan" becomes "Gigantic" (so it doesn't have more letters or syllables than the tip-top "Colossal"), while at the small end, the first two categories get renamed "Wee" and "Veery" (esp., in place of the drawn-out "Diminutive").

• Wee
• Veery
• Tiny
• Small
• Medium
• Large
• Huge
• Gigantic
• Colossal

III. Action types are revised and shortened

The different action types are not terribly well presented, probably too many in number, and a constant source of confusion for intermediate players. (Example: It's hard to understand that "standard" and "full" actions actually take up the same amount of time -- and that the associated movement is actually included "in a standard action", per PH p. 121.) The fact that "move-equivalent actions" are usually seen abbreviated as "MEA" is another sign that the label needs to be shortened.

The most transparent rule would be if, in short, "partial actions" were entirely disposed of. A normal round would allow characters a "standard action" and a separate "moving action"; standard actions could be traded for moving, but not vice-versa (as is the case now, via the circuitous option of the "double move special standard action", per PH p. 126). A character would still have the alternative choice of a "full action" which uses up all activity for the round. A character who is slowed (or readying, etc.) would be restricted to only a "standard action" each round, while a character who is hasted would receive an extra "standard action" each round. Everyone would still get a 5-ft.-step in any turn if no other actual movement took place.

So, what happens to all the deleted "partial actions"? In fact, almost nothing changes from the PC's point of view. Practically all the old attack, magic, moving, and miscellaneous "partial actions" are still available with the exact same effect as a new non-moving "standard action" (especially when running/charging is collapsed: see below). We would introduce one new standard action for the "start full action" option (which basically allows completion of half a full action). Finally, the only significant functional change from any of these suggestions is that the anomalous "partial charge" option would be lost.

Other simplifications at the same time could include:

1. All "charge" and "run" actions are collapsed into a single moving action which allows x2 normal speed (plus any special modifiers to running) in a straight line. Any attack in the same turn must be directed in line with this move and is at either +2 (melee) or -2 (ranged). For the rest of the round, the character suffers a -2 penalty to AC, cumulative if the action is taken multiple times in one round. (I'd call this new action a "charge" -- hustling is one charge action per round, running is two charge actions per round.)
2. The old "double move" action is deleted. A new "disengage" action is introduced: a standard action which makes the character's current space non-threatened, solely for the purpose of their next moving action in the same round.

• "Standard Actions" are separated from any movement.
• "Move-Equivalent Actions" become "Moving Actions".
• "Full Round Actions" become "Full Actions".
• "Partial Actions" are deleted.

• No partial charge is allowed.
• Double move doesn't protect against openings (but "disengage" does).
• Charge and run use same combat and movement modifiers.
• Standard action "start full action" is allowed.

Addendum: d20 Modern

Now that the d20 Modern rulebook and SRD have been released (here: http://www.wizards.com/D20/article.asp?x=msrd), we can see that a few changes made in that system move in the direction of some of my suggestions above. No changes to "attacks of opportunity" or size categories have been made (I. and II. above). But, on the other hand:

The action types in d20 Modern are labeled as "Attack Actions", "Move Actions", and "Full-Round Actions". While not exactly what I suggested above, they are indeed shorter and an improvement on the "move-equivalent action" terminology. "Full Actions" still would have been preferential, I think. "Withdrawing" still allows a double move, which I dislike.

"Partial Actions" have been removed as a category, as I suggested above, which is an excellent streamlining. However, they functionally exist in similar ways, through circumstances that reduce characters to only a single "Attack Action", such as in the surprise round. The "Charge" option has been turned into a full-round action, but is still given the option to use it, with a single move, in an attack-action-only surprise round (i.e., a "partial charge", which I'd like to see deleted). The haste spell has a significant change, no longer giving an extra action, but instead simply one extra attack with a full-round attack, and 30 feet more speed on any move (casting an extra spell is specifically prohibited). The "start/complete full-round action" option has been made into a Move action (instead my suggestion of a Standard Action, above), but that is arguably a reasonable decision.

Addendum: 3.5 Edition

One more update: with the release of D&D version 3.5 in 2003, we see that all the modifications mentioned above in d20 Modern have been folded into the D&D rules, as well. Partial Actions are gone, which is excellent. However, I still think that "attacks of opportunity" should have a shorter name, and that "Withdrawing" should only allow a single move.