Metro 2033

The Good
Scariest game I've played on Steam and probably in my top three ever. Creepy noises and a desolate setting filled with mutated monsters that want to eradicate/eat the last of the human race strangely adds to engaging me even more. Combat and adventures are hard and only the most hardcore types should start their first time around on anything but easy. Ammo is limited so you have to scrounge or get used to fighting with your knife which only makes it scarier. Monster noises are the scariest especially when you've got ten bullets left in your pistol and no healing packs. Ask me how I know that. Heh.

The Bad
The game is sometimes linear but for those with limited time you can finish this game in ten to fifteen hours tops.

The Bottom Line
Scariest game I've played on Steam and probably in my top three ever.