Singularity is currently monopolising the "FPS with a time manipulation gimmick" market- but it certainly wasn't the first to do so. Timeshift allowed us to manipulate the 4th dimension back in late 2007 and wrapped its unique mechanics in a half-decent shooter. Many retailers have cleared their stocks some time ago, but ShopTo are currently willing to part with £7.85 for Saber Interactive's paradox-inducing FPS. This will save you around £3.50 compared to Coolshop.
Timeshift is neither a groundbreaking fantastic FPS by any stretch of the imagination... but it's solid enough. You'll kill vaguely sci-fi opponents in vaguely sci-fi environments with a vaguely sci-fi arsenal, and the premise is about as cliched and uninteresting as you'd expect from the genre. On the other hand, the weapons all work as you'd expect, enemies die when you kill them and circle strafing still works a treat. It's generic- but on the other hand, it works and frequently provides some seriously frantic thrills.
But, of course, Timeshift has an interesting trick up its sleeve: the ability to shift time (no kidding). Your wicked awesome armoured suit not only lets you engage in bullet time (yawn) but also lets you both stop and rewind time while you engage the enemy. Hit by a sticky grenade? Just rewind the world and duck out of the way. Is a powerful foe too tough to handle? Slow things down and put him down from behind. The time control mechanics are actually a lot of fun and provide a genuine boost to an otherwise unremarkable title.
Mixed but generally positive critical reception and a budget price tag might make Timeshift worth a punt for FPS junkies waiting for the next slew of contemporary shooters.