I promised some good points about Wizards of the Coast’s Dungeons & Dragons “fourth edition”.
I like the basic idea of at-will, per-encounter, and per-day abilities.
I’ve written before about the fact that per-X abilities can simply and abstractly simulate the fact that some abilities or “special moves” require specific circumstances. If you don’t like simple and abstract, then that’s bad. But I currently prefer simple and abstract.
Another good thing about many 4e abilities is that they have an alternate effect even when the player fails the die roll. ExploderWizard on ENWorld suggested that all per-X abilities should either work automatically (without a die roll) or an alternate effect if the roll fails. I definitely like that idea.
I think there should also be a general rule for getting to re-use a per-X ability. Like spending some sort of “meta-point”. 4e has some specific rules for this but not a general one.
P.S. Another thing about per-X abilities is that when abilities aren’t perfectly balanced (always the case, but can differ based on circumstance) one doesn’t get repeatedly used to the exclusion of the others.