I guess what I'm saying is, I wish something'd fix the fundamental balance problems in 3.5 instead of touching up the rules a little.
Well, Trailblazer does a better job than most, with their combination of the Rest mechanic, their version of
Action Points, and the Rote / Restricted / Ritual spell division. That, and assuming that only
class balance for encounters matters, from a rules design perspective.
Rest Mechanic: Rests come in two varieties, short and long. Long rests are the traditional night's rest that refreshes all abilities (and restores all hp).
Short rests take 10 minutes, restore all per Rest abilities (Rage, Smite, etc), restore 50% hp, and all Rote Spells. A character can spend an action point to regain 100% hp, all Restricted spells, or one Ritual spell.
Action Points: Six per level that provide basic benefits, as well as the fuel for Action Point Enhancements (gained at 1st and every 3 after). The basic abilities include (incomplete list) roll die and add (open-ended) result to total, re-roll failed d20 check and keep result (and you can add a die to this roll), get a new save against ongoing effect, auto-confirm critical hit, extra standard action, and so on.
The Enhancements include things like larger action dice, more dice per level, bonding magic items (numerical bonuses automatically scale with level), sharing action points, extra action dice under certain circumstances, die result as DR, die result as Dodge AC bonus, die result as bonus damage, and some others. Cool stuff that helps a lot, though not regularly.
Also, action points can be used as rewards, either because the GM activates a fumble, or the PCs complete a quest, act very heroic, or just make the GM laugh. (Yeah, a useful quest reward.)
Spell Division: Rote spells have a single target, a duration 1 min / level or less, and come back with a short rest. All 0-levels, magic missile, scorching ray, and similarly fun-but-not-usually-optimal spells are rote.
Restricted spells have a duration 10 min / level (or more), area effects or multiple targets, and all Conjurations (healing is a part of Necromancy).
Ritual spells are whatever spells the GM wants to make 1 / day. Default ritual spells include Divination / Commune, Teleport, Raise Dead, and anything with an XP cost (or really expensive / unusual material components),.
The slots used for Restricted / Ritual only come back when those spells refresh. This means that a caster is either making his allies stop for the day (unnecessarily), is burning up a lot of Action Points to recover spell slots, or is relying almost exclusively on Rote spells.
It's not perfect (by any means), but it does reduce the problems.
Ultimately, most of the imbalance I've found has been in the actual spell abilities. All the SOS spells make it really easy for one bad die roll to completely end a character, and while TB action points help with that, they can't completely eliminate it.