I frankly probably would have gotten rid of most daily ressources... Healing Surges would have stuck around tho. Would have looked a bit more 4e-SAGA-ish as well. I'd probably have experimented with talent trees, with talents that were class specific, but others that were open to everyone.
I'd probably have kept the 'you get to choose something at every level, no boring dead level' style, but would have kept the number of option per encounter lower so as not to bog down things as much.
Probably more flat bonuses that are always on, but to different things so you can pick what you prefer. Like, if you're a caster, instead of getting a new combat spell you get to pick one to upgrade.
You'd have options to keep your fighter a dumb 'I swing my sword', but you would also be able to make a spell caster that just shoots blasts of flame. Simple shouldn't be wedded to a single archetype.
Rituals would have been emphasized as the long form magic where the more complexe effects happen so as to divorce utility casting from combat casting entirely with Wizards getting features to make it easier on them to use.
Skill Powers to make skill choice more fun.
Would have kept the well defined power sources and the transparent design intent of combat role, with clear secondary. Probably giving a unique mechanic to each power source and a more obvious style to combat roles so that the intersections of two is always a different feel. Also a better explanation of why certain Martial Exploits can't be used all the time to satisfy the grognards.
Clear monster math would have been a thing.
A new paradigm for magic item where you can use ressources to customize them so you can find random items but they aren't utterly useless to you if they're outside a specific parameter. I personally like the idea of the abilities of a magical weapon being in magical gems or something that can be moved from one proper socket to another, possibly with specific planar power sources that can't be mixed together.