
I haven't really thought out solutions to these, but I'll gripe anyway:
Attacks of Opportunity - They bog down combats, and create an incentive against movement in combat, with the exception of Monks and some Rogues. If you turn to run away, and I try to trip you, how do you get to hit me back? :\ I think these should be limited to simple attacks only, no trip/grapple/etc, and should be more easily avoidable.
Tumble - The name bothers me a lot, and I think it should somehow be tied to a feat, like Mobility (I.E. Mobility allows you to use a Balance check to avoid an AoO). And the fact that it's the only skill that
directly affects combat.
Ironclad Class Skills - Why can't a Fighter learn Survival? I'm toying with a House Rule that allows additional Class Skills equal to your Int mod, declared at first level or whenever the Int mod is
permanently increased (not just Ioun Stones).
Goofy Weapons - I've done a fair amount of martial arts, including a number of weapons-based arts. In any interpretation, a Spiked Chain is a horrible weapon. Same for many of the double weapons. Which is why you won't find them in my campaign. (OK, I do have an answer to this one.

)
Grappling - Did I mention martial arts? Five years of grappling does not jibe at all with D&D grappling rules. Why should a pin only last one round? Why can't one grappler submit (or choke out) the other? To top it off, nothing provokes a round of groans from the rest of the players like "I attempt a grapple". Ten minute combats suddenly take most of an hour.
Too Damned Many Rules - At times, I ache for "D&D Lite", a game whose rules can be written in a small booklet, and relies on a good DM for judgement calls. "Why can't I wear leather armor under plate?" "Because the DM said you can't! If you don't like it, go find another game."
Like I said, I don't have answers to all these (or I'd have House Ruled them already

). But these are the major speed bumps on my road to D&D happiness.
Telas