I'm pretty certain I fit the description of an old-school grognard, in that my group universally found 4e distasteful (it nearly broke up the group when we tried it, we all got so uninterested). However there isn't anything in this list...
I'd get rid of base attack values and weapon proficiencies and merge them into weapon skills. I'd compress the classes and use a sub-class system and multiclassing to replicate most of the major archetypes. I'd get rid of AC, use Reflex as the base defense, and make damage resistance the main benefit conferred by armor. I'd get rid of hybrid races and replace them with hybrid templates a la 4e's hybrid classes. I'd make the alignment a ten alignment system with five main alignments and five advanced ones.
that I would find breaks the basic feel of D&D, with the possible exception of armor as damage reduction. Some of it fits nicely into the "add complication in a module" design.
Armor as damage reduction is something that's always appealed to me, but I've tried it in different forms several times and we always ended up rejecting it. To avoid the "guy with dagger can't ever hurt you" effect you end up having to layer on too many complications.
One thing I tried was to have a to-hit roll look at the difference in AC and Reflex (or touch AC if you want). If you hit Reflex it did damage reduction, if you hit AC you skipped damage reduction (hit outside the armor).
But it required messing with all the numbers to balance with the system as it was before, and I decided it wasn't worth the extra number you had to check after every hit in combat (I'm a big fan of simple cinematic combat).
Still, something like that could *theoretically* be added as an optional module.