The one set of rules where I have always considered 3.5E D&D to be lacking are the mechanics for movement and particularly chases. In fact, there are no good rules for movement/running in a chase, since the standard movement rules allow for no variability and thus almost all medium-sized humanoids run at exactly the same pace all of the time. This approach makes for boring chases with pre-determined outcomes and does not mesh well with the more random nature of the game in most others aspects of the rules.
In order to spruce up chases, I have come up with the following mechanic:
Running does not quadruple base speed, but merely triples it. Creatures involved in the chase, however, get to roll a d20 check and gain an extra base speed/10 movement per round for each point by which they beat DC 0.
(Note: The same effect could be achieved by setting the DC at 10 and maintaining the original multipliers, but this would result in frequent subtraction, which is said to be more difficult and slower than addition. Hence the somewhat non-standard DC 0 is used here instead, to avoid subtraction of speed in virtually all circumstances.)
The feat, run, no longer shifts running speed from quadruple to quintuple of base speed, but rather adds a +10 bonus to running checks. Of course, it still provides the +4 bonus to jump checks made with a running start.
Medium Encumbrance and Medium Armor downgrade base speed in the same way as in 3.5E rules. Heavy Encumbrance imposes a -10 penalty in place of reducing the running speed multiplier to 3x base speed (which would be redundant). This replaces their other movement penalties for the purposes of running.
Creatures can take 10 on their running checks in situations, where their life does not directly depend on the outcome. Taking 10 on running checks yields exactly the same results as would be obtained by following the old running rules, which could, therefore, be used when simplicity is desired. Chases, escapes from a collapsing tomb, and other situations, where running speed makes all the difference, however, would be adjudicated using the chase mechanic, since the life of the creatures in question depends directly on their running checks, so taking 10 is impossible.
BTW: This is my first thread on this forum. I generally post on EN World, but was attracted to these boards by the announcement of the Pathfinder RPG, which promises to evolve from 3.5E D&D. Although I have been a loyal D&D fan and used (almost) exclusively official materials thus far, 4E is just not doing it for me, so depending on how these rules develop, for the first time ever I may turn to third party companies to give me my RPG fix.
"Hot Pursuit" is OGL...
-TG
I don't have either of these two products, so I cannot tell how chase/escape/movement/running mechanics work in the said products.
The system I came up with, however, is completely consistent with the core rules and is pretty simple too (though perhaps I would need to present it more clearly).