Now the biggest objections to "everything's at will" are that
- Without a system of shifting conditional advantages, it leads to ability spam. There has to be a reason why an optimizing player might use hurricane kick instead of alternating between fireballing the ranged opponents and uppercutting opponents who jump over the fireball otherwise the third move (and any more moves) is a waste of space and time.
- It doesn't let MC's run attrition / exhaustion scenarios. If the PC's never run low on mana or ammo, then health is the only resource which might cause them to retreat or flee. And within the D&D paradigms of "easy combat-time magic healing" and "retreat is rare and risky, heroes fight to the death", that's almost a nonstarter. With easy at-will combat healing PCs will engage in unlimited workdays.
- It runs afoul of many types of Genre emulation. Not only do the unlimited workdays mentioned above run afoul of much of the source material, there are quite a few works of fantasy where characters have Big Deal attacks that they can do sometimes, but not every round. For example Lina Inverse usually opens with Burst Rondo, Flare Arrow and Fireball and only rarely uses Dragon Slave more than once per episode - even though Dragon Slave is clearly a much upgraded Fireball.
So I'm proposing a vague outline of a hypothetical resource scheme which addresses the above problems (which might not even be problems to everyone) with the idea that something like it potentially could be implemented in a future nonexistant D&D like-game. Of course, this idea is half-baked, and of course any implementation will come with more complexity than everything-is-at-will. Maybe the tradeoffs will look worth it.
Here's the idea: It takes Actions to recharge the better powers.
Always on powers don't recharge, you just get an AC increase from wearing armor, you just get +2 damage from having the Fightgar level that gives you weapon specialization. I don't need to elaborate.
At will powers reload as free actions. They recharge automatically so long as you can take actions. I don't need to elaborate.
What would in 4e terms be called Encounter powers require a character to take a reload action to recharge. For encounter style powers, this reload action is at least as long as attacking with the power and probably involves suffering defensive penalties for the round in which the character reloads. (Because imposing defensive penalties on a recharging character provides at least a small incentive to target someone other than focus fire)
Thus, if you set up encounter-type powers to be actually better than At-Wills, and if you set up your combats to last on average as many rounds as a PC gets encounter-type powers, they will generally burn through each of their encounter powers. But if they have a power that is for some reason double-or-better effective (because the enemies are fire-vulnerable or somesuch), then it's worthwhile for a PC to waste the turn. If a combat goes long (either due to unlucky rolls or MC design), then PCs have the choice of falling back on at-wills every round or recharging their best-in-this-case power to use it every other round. This provides some tactical incentive for individual PCs to withdraw from long fights for a round or two, taking cover to reload while teammates cover them-- And that sort of thing is actually pretty decent genre emulation. This setup also provides a reason for why PCs use moves that aren't the invulnerable flaming uppercut and lets MCs run at least limited exhaustion/overwhelm scenarios by just designing fights to last more rounds than the PCs have encounter-type powers.
Now for powers rarer than encounter-type, we have a couple options. We go go straight 4e and say that they have a recharge time of "Long Rest", meaning you can only use each once per day (or per abuse of the Rest rules at any rate). Or we can do what another poster suggested in one of the numerous 4e rantings, and ditch the notion of "daily" powers for "only one of these powers each encounter". In effect giving characters a fully-charged Super Combo meter or Extreme Gage, that powers their Big Deal Moves, but has a recharge action that requires non-combat time. Keep the noncombat time longer than the longest fight scene but notably shorter than "Long Rest" and you have actually provided an incentive to withdraw from fights not merely for a round or two of breath catching, but actual strategic level regrouping. You also have a setup where sometimes it's worth burning Dragon Slave to nova on round 1, but other times you might want to use Freeze-in-Place and Magic Boost before trotting out your Big Deal attack.
As an added bonus, if you're going vaguely 4e, you can totally have various Buffs and Zones last "until this power is recharged" - freeing you from tracking rounds of durations and yet giving more tactical flexibility than "until end of encounter" would.
*****
Now obviously, this setup will still have some ability spam and a lot of 5-moves-of-doom setups where PCs burn through each of their encounter powers and their Big Deal in the same order and then fall back on at-wills. Also obviously you are limited to either a relatively small number of encounter-type powers or absurdly long combats. So if those are dealbreakers for you, this should be a nonstarter.
