You can make a non-generic FPS the same way you can make a non-generic game in any genre: do something that surprises and pleases the users. You do not surprise the user (though you can still please them) by doing what everybody else is doing, nor by stepping it up a notch. Anybody can make it bigger, better, and more violent, but it takes true genius to go the other way (to paraphrase Grampy's Einstein quote).
Portal is the best example in recent years of an FPS which did this: it's not bigger (quite a bit smaller, actually), it's not better (there's only one gun which can't actually hurt anything by default, and one enemy type), and it's not more violent (there's basically only two ways to even die). But it is brilliant, because it takes the risk of doing something that no FPS has ever done before.
Sky Render - Sanity is for the weak.
