I recently finished Metro 2033 and Singularity. Both are Russian games set in alternate realities. They were both really short I completed both of them in less than 10 hours each.
Of the two I had more fun with Singularity but I liked the atmosphere and weapons of Metro 2033 more.
I played both of them on my PC. Metro 2033 ran pretty well and looked good but Singularity had horrible "Unreal Engine 3" texture pop-in problems and sometimes the textures never popped in making the game look really ugly. This didn't distract from the fun though.
The guns in Metro 2033 were varied and fun and each had its own purpose, in contrast the guns in Singularity are your standard run-of-the-mill FPS guns and I mostly used the machine gun and shotgun.
The time elements in Singularity were a neat gimmick but the fluid shooting and boss battles were excellent. I was also scared a couple of times.
The shooting in Metro 2033 wasn't as fluid but I loved how each mission could be full on run-and-gun or stealth. If I felt like fighting I could but if I wanted to sneak around that was always an option. Singularity was completely linear and there was only one way to do things but it was fun.
I would recommend both games.