Its so good, I can't stop loving it.
I won't spoil any major plot details but I will tell you the setting. After a unnamed war. Nuclear fallout has engulfed the world in nuclear winter and its surviving inhabitants have been driven to the underground metro system (in Russia anyway). And as Artyom, you have to travel through the hostile metro tunnels fighting bandits, mutants and the undead.
A lot of people have stated that the combat in this game is terrible. I on the other hand totally disagree and find it perfectly normal. It may not be as smooth a call of duty, but it is still great. But i have to admit, the stealth in this game is really tricky. If one guy spot you the whole station is on red alert. And I have noticed that there a few glitches and bugs. Not game killers, but just noticeable.
So overall ...
Story 10/10
Gameplay 7/10
Scares 9/10
Also I recommend the book :D