The game casts you as Captain Nate Renko, and at the opening of the game you're heading out to investigate a Russian island called Katorga-12. The research island, as it turns out, is the home of a substance known as Element 99. The mystical element, discovered by Russian scientists in the 1950s, has time-warping properties, and as the result of Russian experiments gone horribly awry, time is sort of ripping at the seams all over the island. So you'll change history, then change it again, and then maybe change it a few more times over the course of the game. The game does a great job of showing how your minor actions fan out to cause global changes to the power structure of the modern world, and the game has a terrific atmosphere to it that made me want to explore every little hallway in search of audio logs and other little things to help fill in the story. Some of the audio logs are better than others, but overall there's enough good story stuff to keep you focused on progressing through the game. The story works because the game's good at feeding you a lot of misdirection. Since you're making changes to the timeline, it's hard to tell who to trust at any given moment.
As you work your way across the island, you'll do a lot of shooting. Most of your targets will be Russian soldiers, but there are plenty of messed-up time creatures to dispatch along the way. The game gives you some decent standard weapons to use, like an assault rifle, pistol, shotgun, or minigun. But then you've got the sniper rifle, which has a slow-motion feature that makes taking down distant enemies a breeze. Then there's a grenade launcher, which has an alternate mode that fires out a glowing ball that you can control, allowing you to roll grenades right up to enemies before taking them out. Or the spikeshot, which is a railgun of sorts that fires charged-up slugs that explode shortly after impact. Though you can swap most of these weapons around at will by visiting a weapon station, you also encounter a couple of weapons that are limited-use guns that aren't stored. The coolest of these is the seeker, which is a rifle that fires single shots. The catch is that time slows down when you fire these shots and the game gives you a bullet's eye view of the action, letting you steer your shots into your targets. It's pretty cool.
While the campaign is the main reason to check out Singularity, the multiplayer's pretty decent. The extermination mode pits a team of human players against a team of creepy time monsters in an objective-based match. Playing as the enemy is pretty interesting, and the whole thing is class-based. So you can play as a healer, use teleport abilities, and so on. You can even play as a Phase Tick, which is a little crawling enemy that might as well be the Ticker from Gears of War. When playing as the Phase Tick, you can possess human soldiers, giving you the ability to kill the human team with their own weapons. It's a bit monotonous, and it only has two modes, but the multiplayer's still OK.
So yeah, what passes for puzzles in the world of Singularity could have been done better, and little things like the way you have to stand near audio logs in order to hear them (which slows down the pace of the game a bit) are sort of annoying. But the action is solid and the story is interesting enough to make Singularity worth checking out.