It just occurred to me while archive-diving Shangrila Towers (Blogroll +1 - god-DAMN) that Painkiller hit on the achievement concept back in 2004.
Painkiller mixes up the distilled classic FPS formula a bit by including the tarot card system; each card provides a minor ability that is either passive and contextually activated, or activated with a hotkey. The abilities are not terribly useful (with exceptions) but do have noticeable utility. Each level in that game features a bonus objective; the reward for completing these is a mildly useful tarot card.
What makes this very much like the achievement system is:
- The objectives are often far from the orthodox way to play. For instance, corpses drop 'souls' when they fade out; these give a minor health boost and charge up a temporary Killing Spree mode that is shockingly reminiscent of Rise of the Triad's take on God Mode. The objective in one level is to not pick up any souls, and since these litter the battlefield after an engagement, this is harder than it sounds.
- There is a difficulty spread from "happens accidentally" to "frigging impossible."
- The reward, while providing a tangible gameplay benefit, is limited enough that the primary reason for unlocking the bonus objective is ego points or completionism.